Patent Publication Number: US-10787381-B2

Title: Drainless reverse osmosis water purification system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS DATA 
     This application is a continuation of U.S. patent application Ser. No. 15/179,108 filed on Jun. 10, 2016, which is a continuation of U.S. patent application Ser. No. 13/663,396 filed on Oct. 29, 2012, now U.S. Pat. No. 9,371,245, which is a continuation-in-part of U.S. patent application Ser. No. 12/795,342 filed on Jun. 7, 2010, now U.S. Pat. No. 8,298,420, which is a division of U.S. patent application Ser. No. 11/870,316 filed on Oct. 10, 2007, now U.S. Pat. No. 7,837,866, which claims priority from U.S. Provisional Patent Application No. 60/829,178 filed on Oct. 12, 2006 and U.S. Provisional Patent Application No. 60/951,265 filed on Jul. 23, 2007, all of which are incorporated by reference herein in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to improvements in water purification systems of the type having a reverse osmosis (RO) unit or the like for removing dissolved ionic material and other contaminants from an ordinary supply of tap water or the like. More particularly, this invention relates to an improved water purification system having a reverse osmosis unit adapted for providing a supply of relatively purified water over a significantly extended operating life, and wherein water waste during normal system operation is substantially eliminated. 
     Water purification systems in general are well-known in the art of the type having a reverse osmosis (RO) unit or membrane for converting an incoming supply of ordinary tap or feed water into relatively purified water for use in cooking, drinking, etc. In general terms, the reverse osmosis unit comprises a semi-permeable RO membrane through which a portion of the tap water supply is passed, such that the membrane acts essentially as a filter to remove dissolved metallic ions and the like as well as other contaminants and undesired particulate matter from the tap water. In normal operation, these impurities are removed from one portion of the water flow and concentrated in another portion of the water flow, commonly referred to as retentate or brine, which is normally discharged as waste to a drain. The thus-produced flow of relatively purified water is available for immediate dispensing for use, and/or for temporary storage within a suitable reservoir or vessel awaiting dispensing for use. A pure water dispense faucet mounted typically on or adjacent to a kitchen-type sink or the like is manually operable to dispense the produced purified water. While the specific construction and operation of such RO water purification systems may vary, such systems are exemplified by those shown and described in U.S. Pat. Nos. 4,585,554; 4,595,497; 4,657,674; and 5,045,197. 
     One disadvantage associated with reverse osmosis purification systems relates to the fact that retentate or brine outflow from the RO membrane is normally discarded as waste. In a typical RO system operating under standard domestic water supply pressures, the ratio of brine outflow to produced purified water outflow can be on the order of about 4:1. Accordingly, the discarded brine flow is sometimes perceived as a relatively substantial waste of water which can be significant in areas wherein the water supply is limited. As a result, many residential and commercial water customers have favored use of bottled water as a purified water source, despite the costs and inconveniences associated with delivery, storage and changeover of large (typically 5 gallon) water bottles with respect to a bottled water cooler. 
     Another disadvantage associated with reverse osmosis systems relates to the typically limited service life of the RO membrane and other pre-filter and post-filter elements typically associated therewith. More specifically, many RO systems use a pre-filter element typically including a carbon-based filtration media for removing some contaminants from a tap water inflow at a location upstream from the RO membrane. One important function of this pre-filter element is to remove contaminants that would otherwise shorten the operating service life of the RO membrane. A downstream-located post-filter element is also commonly provided for additional water filtration and purification before dispensing. This array of pre- and post-filter elements, in combination with the RO membrane, is often provided in the form of individual cartridges designed for facilitated disassembly from and re-assembly with a unitary-type manifold. See, for example, U.S. Pat. No. 5,045,197. Despite the fact that cartridge replacement may be required only once each year, and despite efforts to make cartridge changeover an intuitively simple process, many customers are reluctant to handle this task. Instead, replacement of the various RO system cartridges has largely remained the responsibility of a water service company, thereby entailing regular and relatively costly service calls to each customer&#39;s residence or place of business. The requirement for regular service calls dramatically increases the overall operating cost of the RO system, thereby reducing or eliminating apparent advantages relative to conventional bottled water coolers and related bottle delivery systems. 
     There exists, therefore, a significant need for further improvements in and to reverse osmosis water purification systems, wherein water waste is substantially eliminated, and further wherein the service life of a reverse osmosis (RO) membrane is significantly extended for at least a period of several years without requiring attention by service personnel. The present invention fulfills these needs and provided further related advantages. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, an improved drainless reverse osmosis (RO) water purification system is provided to produce relatively pure water for on-demand dispensing, while recycling retentate or brine in a manner which substantially eliminates water waste. The improved RO system further includes a catalyst pre-filter for treating a tap water supply to remove contaminants, particularly such as chlorine-based contaminants, prior to or upstream from a reverse osmosis (RO) membrane, thereby significantly extending the service life of the RO membrane, and wherein this catalyst pre-filter is regularly refreshed or renewed to provide a compatible extended service life. In addition, the RO membrane is incorporated into a multi-cartridge unit including an additional pre-membrane filter element and a post-membrane filter element, wherein this multi-cartridge unit is adapted for quick and easy slide-out removal and slide-fit installation of a replacement unit, when and if required. Moreover, the RO system may further include a source of filtered, relatively purified air. 
     In the preferred form, the catalyst pre-filter is coupled to a conventional and typically cold tap water supply source. The catalyst pre-filter carries a supply of a catalyst in particulate form, such as a copper-zinc media. During normal operation of the RO system to produce relatively purified water, a relatively slow tap water flow proceeds upwardly through the catalyst particulate, at a rate and pressure insufficient to disturb the catalyst bed, resulting in catalyzation of chlorine-based contaminants such as chlorine and chloramines to other forms not harmful to the RO membrane, as well as retention of particulate contaminants. The catalyst pre-filter is also coupled in-line between the tap water supply source and a conventional tap water cold dispense faucet. Each time the cold dispense faucet is turned on at a typical, relatively high flow rate, the tap water upflow through the catalyst particulate functions to lift and stir the particulate from the settled bed to a substantially fluidized and turbulently intermixing state. As the particulate turbulently intermixes, the catalyst particles abrade for removal of surface oxidation and are thus renewed or refreshed. The catalyst particulate is retained within the catalyst pre-filter, whereas the removed oxidation and any entrapped particulate contaminants are flushed with the water flow to and through the cold water dispense faucet. 
     During pure water production, the catalyst pre-filter discharges a filtered tap water outflow to the multi-cartridge unit, for series flow to the pre-membrane filter element, the RO membrane, and the post-membrane filter element. The pre- and post-membrane filter elements may include a carbon-based filtration media. The RO membrane separates the water flow into a relative purified water outflow having contaminants substantially removed therefrom, and a retentate or brine outflow having the contaminants substantially concentrated therein. In accordance with one aspect of the invention, the brine outflow is not discharged as waste to a drain, but is instead pumped to a hot water circuit forming a portion of a domestic water supply system. As such, the brine outflow is recycled in a manner whereby recirculation thereof to the RO membrane is substantially eliminated. 
     The produced purified water is available for immediate dispensing as by means of a pure water dispense faucet. Alternately, the produced purified water is directed to and stored within a pure water reservoir awaiting dispensing via the pure water dispense faucet. In the preferred form, water flowing to the pure water dispense faucet may be further subjected to a final catalyst filter having a particulate media including zinc to enhance water freshness and sanitation. 
     A control valve monitors the volume of water contained within the pure water reservoir, and functions to disconnect the brine outflow from the hot water system when the pure water reservoir reaches a substantially filled condition and pure water production ceases. In this mode, the tap water inflow to the RO membrane flows untreated to the brine outflow side and is continuously recirculated by the control valve between the catalyst pre-filter and the RO membrane. Upon resumed pure water production, the control valve re-directs the brine port outflow to the hot water system. In one preferred form, the control valve comprises a pressure-responsive valve assembly for shifting the water outflow from the RO membrane brine port in response to water pressure within the pure water storage reservoir. 
     The multi-cartridge unit including the RO membrane and the pre- and post-membrane filter elements is provided as a unitary device adapted for quick and easy removal from and replacement within a manifold housing, in a unidirectional or one-way installation with the cartridges properly connected to system plumbing lines. In the preferred form, the multi-cartridge unit is adapted for one-way drop-in mounting into a housing drawer adapted for slide-out displacement for access to and removal of the cartridge unit. A replacement multi-cartridge unit is drop-fit installed into the housing drawer which is then slidably advanced into the manifold housing in proper coupled relation with the system plumbing lines. 
     The manifold housing may additionally include an air filtration system including a removably mounted air filter and a fan for drawing air over the air filter for purification. Filtered air is coupled from the manifold housing to the pure water dispense faucet to provide relatively purified air in the same room within which the purified water is available. 
     The RO system may further include a conductivity monitor system of the general type including water-contacting electrodes and indicator means such as one or more indicator lights on the pure water dispense faucet for indicating a need to replace the RO membrane. In the preferred form, the indicator lights are adapted to provide a first color (such as green or blue) when the pure water faucet is open and the RO membrane is functioning properly, and a second color (such as yellow or red) to indicate a need for RO membrane replacement. In the preferred form, the monitor system will illuminate the second color continuously, as by continuous lighting or continuous blinking of the second color until the RO membrane is replaced. In an alternate preferred form, the monitor system is programmed for illuminating the first and second colors in an alternating blinking sequence until the RO membrane is replaced. The pure water dispense faucet may further incorporate a photocell for detecting ambient light intensity, and for operating one or more of the indicator lights in a night-light limited illumination mode. 
     Upon replacement of the multi-cartridge unit, to replace the RO membrane, the monitor system is re-set. In a preferred form, such resetting occurs by providing each multi-cartridge unit with a unique code carried thereby, such as a unique bar code printed on a label on the multi-cartridge unit at a predetermined location. A reader mounted on or within the manifold housing is responsive to the unique code on the multi-cartridge unit, for resetting the conductivity monitor system. That is, removal of a multi-cartridge unit followed by re-installation of the same unit will not re-set the monitor system. But installation of a different multi-cartridge unit having a different unique code thereon will re-set the monitor system. 
     Other features and advantages of the present invention will become apparent from the following more detailed description, taken in connection with the accompanying drawing which illustrate, by way of example, the principals of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate the invention. In such drawings: 
         FIG. 1  is a schematic diagram illustrating a drainless reverse osmosis water purification system embodying the novel features of the present invention; 
         FIG. 2  is an enlarged vertical sectional view of a catalyst pre-filter cartridge for use in the invention, and depicting a particulate catalyst in a normal settled bed orientation for pure water production; 
         FIG. 2 a    is a vertical sectional view of the catalyst pre-filter cartridge, similar to  FIG. 2 , but showing the particulate catalyst in a turbulently agitated flush-flow mode for catalyst renewal; 
         FIG. 3  is an enlarged perspective view showing an exemplary manifold housing for use in the invention; 
         FIG. 4  is an enlarged perspective view of the manifold housing of  FIG. 3 , with a housing cover removed to illustrate internally mounted components, and with a slidably retractable drawer carrying a removably mounted multi-cartridge unit including a reverse osmosis (RO) cartridge; 
         FIG. 5  is an alternative perspective view of the manifold housing similar to  FIG. 4 , with the housing cover removed and showing the slide-out drawer with multi-cartridge unit in a fully installed position; 
         FIG. 6  is a further perspective view of the manifold housing similar to  FIGS. 4 and 5 , but illustrating the slide-out drawer in a retracted or open state, and showing the removable multi-cartridge unit in exploded relation therewith; 
         FIG. 7  is an enlarged fragmented cross-sectional view taken generally on the line  7 - 7  of  FIG. 5 ; 
         FIG. 8  is a vertical sectional view taken generally on the line  8 - 8  of  FIG. 5 ; 
         FIG. 9  is a schematic flow diagram indicating water flow through the manifold housing including the multi-cartridge unit removably installed therein; 
         FIG. 10  is an enlarged vertical sectional view showing internal details of a control valve mounted within the manifold housing, wherein the illustrative control valve conforms with one preferred embodiment of the invention; 
         FIG. 11  is an enlarged vertical sectional view showing a final catalyst filter cartridge mounted within the manifold housing; 
         FIG. 12  is an enlarged vertical sectional view depicting a pure water dispense faucet for use in the invention; 
         FIG. 13  is an exploded perspective view of the pure water dispense faucet of  FIG. 12 ; 
         FIG. 14  is a front elevation view of the pure water dispense faucet of  FIG. 12 ; 
         FIG. 15  is a schematic circuit diagram showing a conductivity monitor system and related control components; 
         FIG. 16  is an enlarged vertical sectional view showing an alternative control valve constructed in accordance with one alternative preferred embodiment of the invention, and showing the control valve in relation to a portion of the system plumbing circuit; 
         FIG. 17  is an enlarged vertical sectional view showing a further alternative form of a control valve constructed in accordance with the invention, and showing the modified control valve in relation to a portion of the plumbing system; 
         FIG. 18  is an enlarged vertical sectional view, in somewhat schematic form, depicting a reverse osmosis cartridge including means for adding one or more selected minerals to produced purified water, in accordance with one alternative preferred form of the invention; 
         FIG. 19  is an enlarged exploded and fragmented perspective view showing a modified reverse osmosis membrane assembly for use in the modified reverse osmosis cartridge of  FIG. 18 ; 
         FIG. 20  is an enlarged vertical sectional view showing, somewhat in schematic form, a further alternative control valve constructed in accordance with one further alternative preferred embodiment of the invention; 
         FIG. 21  is a fragmented perspective view similar to  FIG. 3 , but depicting a modified manifold housing having an improved latch mechanism for controlling movement of the cartridge-carrying retractable drawer between a secure normally closed position and an open position, with a front panel on the retractable drawer being depicted in a partially open position; 
         FIG. 22  is a fragmented vertical sectional view taken generally on the line  22 - 22  of  FIG. 21 , but showing the retractable drawer in the secure normally closed position; 
         FIG. 23  is a fragmented vertical sectional view similar to  FIG. 22 , but illustrating the retractable drawer is the partially open position; and 
         FIG. 24  is an enlarged fragmented perspective view similar to  FIG. 21 , but with the drawer front panel removed for illustrating components of the improved latch mechanism. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in the exemplary drawings, an improved reverse osmosis (RO) water purification system referred to generally in  FIG. 1  by the reference numeral  10  includes a reverse osmosis (RO) cartridge  12  having a reverse osmosis (RO) membrane therein for separating a tap water inflow into relatively purified water  14  available for on-demand dispensing, and a so-called retentate or brine flow having contaminants and impurities substantially concentrated therein. In accordance with the invention, during pure water production, the brine flow is recycled to a hot water side or hot water circuit of a domestic water supply system to avoid water waste. In addition, tap water inflow to the RO cartridge is pretreated by flow through a catalyst pre-filter  16  to catalyze chemical contaminants which would otherwise be harmful to the RO membrane, thereby significantly increasing the service life of the RO membrane. A particulate catalyst  18  within the catalyst pre-filter  16  is periodically refreshed to achieve extended service life compatible with the extended service life of the RO membrane. 
     The illustrative reverse osmosis water purification system  10  is designed to provide a ready supply of substantially purified water  14  for drinking and cooking purposes, etc. The system  10  is generally designed for residential or household use, or for use in a commercial facility particularly such as an office or the like, installed typically within the compact cabinet space located beneath a kitchen-type sink (not shown) or the like, with a pure water dispense faucet  20  normally mounted on a countertop  21  on or adjacent the sink for on-demand pure water dispensing. In this regard, the pure water dispense faucet  20  is typically installed alongside or in close proximity with a conventional faucet or faucet set  22  including cold and hot water faucet valves  24  and  26  operable for respectively dispensing untreated cold water and untreated hot water, or a tempered mixture thereof, through one or more dispense spouts  27 . 
     A standard domestic water supply system includes a tap water supply  28  coupled to a cold water circuit  30  to which the cold water faucet valve  24  is also connected. The tap water supply  28  is additionally coupled through a water heater  32  to a hot water circuit  34  to which the hot water faucet valve  26  is connected. Persons skilled in the art will appreciate that the illustrative cold and hot water circuits  30 ,  34  will normally incorporate multiple hot and cold water dispense sites, each with a corresponding dispense faucet set  22  or the like. In addition, persons skilled in the art will recognize that single-handle faucet sets can be used for dispensing cold water, hot water, or a tempered mixture thereof. 
     In general, the purification system  10  receives a tap water inflow by coupling the catalyst pre-filter  16  into the domestic cold water circuit  30 . During normal operation, this cold tap water inflow passes through the catalyst pre-filter  16  at a relatively slow flow rate for treatment, and the thus-treated water is delivered to a multi-cartridge unit  36  which includes the RO cartridge  12  having the RO membrane contained therein. The RO membrane within the RO cartridge  12  separates the tap water inflow into the produced relatively purified water  14  which is delivered to a storage reservoir  38  where it is available for on-demand dispensing, and the retentate or brine flow which is normally recycled through a recycle conduit  40  to the hot water side of the domestic water system. 
     In this regard, persons skilled in the art will recognize and appreciate that the purified water  14  has impurities substantially removed therefrom, whereas these removed impurities are retained within and carried off by the retentate or brine flow for recycling to the water supply system, and in the preferred embodiment, to the hot water circuit  34  of the water supply system. While the term brine is commonly used to refer to this retentate flow, persons skilled in the art will understand that the level of impurities carried by this brine flow does not render the water toxic or harmful for a wide range of traditional domestic water supply uses such as washing, bathing, etc. Indeed, when this retentate or brine flow is intermixed with other water within the water supply system, the proportional increase in overall impurities is virtually unnoticeable. 
     In accordance with one primary aspect of the invention, the catalyst pre-filter  16  includes the particulate catalyst  18  ( FIG. 2 ) for pre-treating the tap water inflow in a manner to effectively catalyze chemical contaminants known to be harmful and thus known to significantly reduce the service life of the RO membrane within the RO cartridge  12 . Such chemical contaminants commonly include chlorines and chloramines which are commonly present in domestic water supplies. Importantly, this particulate catalyst  18  is regularly refreshed or renewed by a rapid flush-flow of the cold tap water supply through the catalyst pre-filter  16  each time the cold water faucet valve  24  is turned on for a substantial cold water flow rate. Accordingly, the service life of the particulate catalyst  18  is also significantly extended for compatibility with extended service life of the RO membrane, with a preferred service life for these components being on the order of about 5-7 years. 
       FIG. 2  shows the catalyst pre-filter  16  is more detail. As shown, the catalyst pre-filter  16  comprises an upright housing  42  which may have a generally cylindrical cross sectional shape, to include a lower multi-port fitting  44  defining a tap water inflow port  46  connected to the cold water supply circuit  30 . Cold tap water is thus available to flow through this inflow port  46  and upwardly through a lower inlet filter screen  48  of generally upwardly projecting conical geometry into an internal pre-filter chamber  50 . This pre-filter chamber  50  is partially filled with the particulate catalyst  18 , with  FIG. 2  showing this particulate catalyst in the form of a settled bed occupying up to about ½ of the volume of the pre-filter chamber  50 . This particulate catalyst  18  comprises, in a preferred form, a metal-based particulate including copper and zinc components, with one preferred catalyst material being available from KDF Fluid Treatment, Inc., of Constantine, Mich., under product designation KDF-55. See also U.S. Pat. No. 5,135,654, which is incorporated by reference herein. 
     During normal pure water production, with the cold water faucet valve  24  in a normally closed position, the tap water inflow into the pre-filter chamber  50  proceeds upwardly as indicated by arrow  51  into and through the settled catalyst bed at a relatively slow flow rate which is insufficient to disturb or disrupt the particulate catalyst  18  from the illustrative settled bed. As a result, the water-catalyst contact or residence time is substantial, and sufficient for substantially thorough catalyzation of chemical contaminants as by oxidation reduction reaction. Particulate contaminants are also trapped within the catalyst bed, and thereby removed from the water upflow therethrough. The treated water flow then proceeds upwardly through the open upper portion of the pre-filter chamber  50 , and through an upper filter screen  52  into a small head space  54  before turning downwardly for passage through a spiral-wrapped and/or pleated filter element  56  positioned annularly about the pre-filter chamber  50 . A stainless steel mesh material may also be used for the filter element  56 . The filter element  56  is adapted to trap additional particulate contaminants, preferably to a size of about 5 microns, before coupling the water flow to a first lower water outflow port  58  formed as a portion of the lower multi-port fitting  44 . From this outflow port  58 , the pre-treated water is delivered to the multi-cartridge unit  36  including the RO cartridge  12  for pure water production, as will be described in more detail. Persons skilled in the art will understand that the filter element  56  is optional, wherein the size of the catalyst particles may be chosen to entrap and retain small-sized particulate contaminants. 
     The particulate catalyst  18  is especially effective in catalyzing chlorine-based chemical contaminants of the type commonly present in many domestic water supply systems for sanitizing the water supply. Such constituents are harmful to a semi-permeable membrane of the type used in the RO cartridge  12  for pure water production, typically resulting in a dramatically shortened membrane service life. By catalyzing these chemical contaminants to a form that is not harmful to the RO cartridge  12 , the service life of the RO membrane dramatically increases. Such catalyzation is accompanied by an oxidation reduction reaction which results in an oxidation layer on the catalyst particles, wherein, over time, this oxidation layer can obstruct or interfere with good water-catalyst contact. Accordingly, over a period of time, the effectiveness of the particulate catalyst  18  can be significantly diminished. 
     To avoid this reduction in catalyst effectiveness, the particulate catalyst  18  is regularly renewed or refreshed by removing the oxidation surface layer therefrom and flushing this removed oxidation and any trapped particulate contaminants from the pre-filter  16 . This is accomplished by connecting the catalyst pre-filter  16  via a second lower water outflow port  60  to the cold water faucet valve  24  via the cold water circuit  30 . In this regard, normal installation of the water purification system  10  into the cabinet space underneath a sink having the faucet set  22  mounted thereon conveniently positions the pre-filter  16  close to the faucet set for quick and easy flush-flow to renew the catalyst  18 . Accordingly, when the cold water faucet is turned on periodically with a substantial flow rate, the upflow passage of tap water through the pre-filter chamber  50  is dramatically increased and is sufficient to lift and turbulently stir the particulate catalyst  18  throughout the entire chamber volume, as viewed in  FIG. 2 a   . As this rapid flush-flow occurs through the pre-filter chamber  50 , the catalyst particles tumble and abrade against one another in the form of a turbulent fluidized bed, thereby abrading off the formed oxidation layer thereon for flush-flow of this oxidation layer with the water past the upper filter screen  52  and further through the second outflow port  60  to the cold water faucet  24 . Importantly, as a result, the particulate catalyst  18  is effectively renewed or refreshed for enhanced effectiveness with an extended service life compatible with the extended service life of the RO membrane. In one preferred form, the filter element  56  is omitted (as previously noted) to avoid clogging thereof by flushed oxidation and other entrapped contaminant particles. Upon closing the cold water faucet valve  24 , this rapid flush flow through the catalyst  18  ceases, and the slow pure water production flow resumes thereby allowing the catalyst particles to re-settle into the bed configuration shown in  FIG. 2 . 
     While the illustrative drawings show the conical filter screen  48  at the lower end of the pre-filter chamber  50 , persons skilled in the art will appreciate that alternative water inflow geometries into contact with the particulate catalyst  18  may be used. Such alternative water inflow configurations may include, but are not limited to, upwardly jetted arrangements conducive to substantially thorough fluidization of the particulate catalyst  18  when the cold water faucet valve  24  is turned on, and for substantially thorough water-particulate contact without fluidization during pure water production with the cold water faucet valve  24  turned off. 
     The multi-cartridge unit  36  including the RO cartridge  12  is removably installed into a compact manifold housing  62 , as shown best in  FIGS. 3-6 . As shown in accordance with a preferred form, the multi-cartridge unit  36  comprises a trio of cartridges including the RO cartridge  12  having the RO membrane therein, in combination with a pre-membrane filter cartridge  64  and a post-membrane filter cartridge  66  ( FIGS. 4-6 ). This trio of cartridges  12 , 64  and  66  are preassembled on a manifold base  68  configured to define a predetermined sequential flow path for water flow to and through these cartridges  12 , 64  and  66 . The manifold base  68  carries a ported end plate  70  for slide-fit connection with a pair of cylindrical alignment pins  71  and a plurality of cylindrical water conduit members  72  ( FIGS. 4 and 6-7 ) protruding from a fixed manifold  74  within the housing  62 . A handle  75  conveniently interconnects the upper ends of the three cartridges  12 , 64  and  66  for facilitated manual grasping and manipulation of the multi-cartridge unit  36  for quick and easy drop-fit installation into or lift-out removal from the housing  62 . 
     In one preferred form, this handle  75  is constructed from a flexible fabric material such as canvas belt of the like suitable for easy manual grasping, but collapsible upon release to occupy minimal space within the manifold housing  62 . Accordingly, the collapsible handle  75  permits use of cartridges  12 ,  64  and  66  of substantially maximum or optimized heights, thereby further enhancing the service life of the multi-cartridge unit  36 . 
     As shown best in  FIGS. 4 and 6 , the housing  62  includes an internal base  76  having the fixed manifold  74  mounted generally at an inboard end thereof. An extensible slide unit  78  is mounted on this internal base  76  for supporting a drawer  80  adapted for sliding movement between an advanced or closed position within a manifold cover  81  ( FIGS. 3 and 5 ) and an open or retracted position ( FIGS. 4 and 6 ) with a portion of the drawer  80  exposed at a front end of the manifold housing  62 . This movable drawer  80  defines an upwardly open pocket  82  ( FIG. 6 ) for drop-in reception of the manifold base  68  of the multi-cartridge unit  36 . A front margin of the drawer  80  carries a closure panel  84  with a drawer pull  86  thereon for facilitated manual movement of the drawer  80  between the open and closed positions. The drawer pocket  82  ( FIG. 6 ) is defined by irregular surfaces such as the illustrative triangular indents  88  formed at longitudinally off-center positions along the drawer length, for mated reception into notches  90  formed in the sides of the manifold base  68 , thereby assuring unidirectional or one-way drop-in reception of the multi-cartridge unit  36  into the drawer  80 . 
     With the multi-cartridge unit  36  seated within the open drawer  80 , as viewed in  FIG. 4 , the drawer  80  can be closed by simple slide-in action to displace the ported manifold end plate  70  into fluid-coupled relation with the plurality of water conduit members  72  on the fixed manifold  74 . The guide pins  71  are designed to engage reciprocal bores (not numbered) in the end plate  70  to correctly align the slidable manifold base  68  with the fixed manifold  74  such that engagement between the end plate  70  and the water conduit members  72  automatically functions to provide the correct fluid flow paths for proper operation of the reverse osmosis water purification system  10 . Persons skilled in the art may recognize that other alignment mechanisms may be used in place of or in addition to the guide pins  71 .  FIG. 7  illustrates construction details of one exemplary and preferred coupling arrangement, wherein multiple ports  92  formed in the end plate  70  each include a check valve  94  spring-loaded to a normally closed position to prevent water leakage therefrom. Each of these check valves  94  is adapted for push-fit engagement and partial retraction by a probe  95  of the associated one of the water conduit members  72  which carries one or more seal rings  96  for slidably sealed engagement within the end plate port  92  prior to opening movement of the associated check valve  94 . Similarly, each of the water conduit members  72  is mounted on the fixed manifold  74  for accommodating a short axial retraction stroke of the associated probe  95  upon registration with the check valve  94  of the associated end plate port  92 , for displacing a second, normally closed spring-loaded check valve  98  (within the fixed manifold  74 ) to an open position. Accordingly, slide-fit coupling of the end plate ports  92  with the water conduit members  72  is accompanied by opening of the check valves  94 ,  98  to permit water flow, whereas slide-out separation of these components is accompanied by spring-loaded re-closure of the check valves  94 ,  98  to prevent water leakage.  FIG. 8  shows the multi-cartridge unit  36  installed within the drawer  80 , with the drawer  80  slidably advanced to the closed position for assembling the ported end plate  70  in flow-coupled relation with the water conduit members  72  of the fixed manifold  74 . 
     With the multi-cartridge unit  36  installed into the manifold housing  62 , with the cartridge manifold base  68  in flow-coupled relation with the fixed manifold  74 , production of pure water proceeds in a normal manner. In this regard, as shown in somewhat schematic form in  FIG. 9 , the fixed manifold  74  receives the water outflow from the catalyst pre-filter  16 , via a flow conduit  100  from the first lower outflow port  58  of the catalyst pre-filter  16  (see also  FIG. 1 ). The fixed manifold  74  couples this pre-treated water flow to the cartridge manifold base  68  for initial flow to and through a flow path  101  to the pre-membrane filter cartridge  64 . In the preferred form, this pre-membrane filter cartridge  64  includes a conventional carbon-based filtration media  102  such as granulated carbon for capturing residual contaminants that may be present in the otherwise pre-treated water inflow. From the pre-membrane filter cartridge  64 , the manifold base  68  routes the filtered water flow via a flow path  103  to a tap water inflow port for supplying the water flow to the RO cartridge  12  having a conventional semi-permeable RO membrane  104  therein. During pure water production, the RO membrane separates the water inflow into two water outflows, namely, relatively purified water coupled via a purified water outflow port to a first RO outlet flow path  106 , and brine coupled via a brine outflow port to a second RO outlet flow path  108 . 
     The produced relatively purified water  14  is coupled via the first RO outlet flow path  106  via a flow path  107  in the manifold base  68  to the post-membrane filter cartridge  66 . The post-membrane filter cartridge  66  also includes a conventional carbon-based filtration media such as granulated carbon  110  for capturing residual contaminants in the pure water stream. From this post-membrane filter  66 , the purified water  14  is coupled to a flow path  112  through the manifold base  68 , and in parallel with the brine outflow at the second RO outlet flow path  108 , to the fixed manifold  74 . The fixed manifold  74 , in turn, defines internal flow paths  109  and  111  for coupling the filtered pure water path  112  and the brine path  108  respectively to a control valve  114 . 
     The control valve  114  is mounted on the fixed manifold  74  within the housing  62  for direct water-flow connection thereto. As shown in  FIG. 10  in accordance with one preferred form, the control valve  114  comprises a multi-chambered valve housing  116  defining a pure water inflow port  118  and a pure water outflow port  120  at opposite ends thereof. The pure water inflow port  118  couples the purified and filtered water flow  14  via the flow path  109  for normal pressure-caused retraction of a seal stop  122  carried at one end of an elongated valve spool  124 , thereby retracting the seal stop  122  from a seat  126  on the valve housing  116  and permitting pure water inflow into a first control valve chamber  128 . Within this first control chamber  128 , the pure water  14  flows past the seal stop  122  to a laterally open entry port  130  formed in the valve spool  124 . The pure water  14  flows through this entry port  130  and into an elongated spool bore  132  for flow to the opposite end of the valve spool  124  and passage therefrom through the pure water outlet port  120  for dispensing and/or storage, as will be described in more detail. 
     The valve spool  124  is biased as by a spring  134  for normally advancing the seal stop  122  into engagement with the associated seat  126 , in the absence of pure water production inflow via the pure water inflow port  118 . Accordingly, when pure water is being produced, sufficient pressure at the inflow port  118  causes the seal stop  122  to retract from the seat and permit pure water inflow, as described. At the same time, brine outflow from the second RO outlet flow path  108  is delivered via the flow path  111  and a flow conduit  135  through a pump  136  ( FIGS. 1 and 9 ) to a central inflow port  138  ( FIG. 10 ) on the control valve  114  for entry into a central valve chamber  140 . This brine inflow passes, during pure water production, upwardly past a now-open recycle valve  142  on the retracted valve spool  124  into an overlying recycle chamber  144  for flow further through an outflow port  146  and the recycle conduit  40  to the domestic hot water circuit  34  ( FIG. 1 ). 
     Conversely, when pure water production is halted, such as when the reservoir  38  is filled to a predetermined volume (as will be described), the spool valve  124  advances the seal stop  122  into seated engagement with the associated seat  126 . At the same time, the recycle valve  142  advances to engage and seat with a housing wall  148  separating the central chamber  140  from the overlying recycle outflow chamber  144  to prevent water flow from the central chamber  140  past said recycle valve  142 . Such closure of the recycle valve  142  is accompanied by, or immediately followed by, opening movement of a recirculation valve  150  also carried by the valve spool  124  and associated with a valve seat  152  to permit water from the central chamber  140  to flow downwardly into an underlying recirculation chamber  154  from which the water flows outwardly via an outflow port  156  for recirculation via a recirculation flow conduit  158  to the catalyst pre-filter  16  (see also  FIG. 1 ). 
     Accordingly, during normal production of pure water  14 , the brine flow having the contaminants concentrated therein is continuously recycled via the pump  136  and control valve  114  through the recycle conduit  40  to the domestic hot water circuit  34 .  FIG. 1  shows the recycle conduit coupled into a hot water circuit conduit at a location near the hot water dispense faucet  26 . Persons skilled in the art will recognize that alternative coupling locations may be used, such as by connecting the brine flow directly to the hot water heater tank  32 . In either case, the brine flow is not wasted, but is instead combined with system hot water, with conventional and typically routine or regular hot water dispensing effectively precluding any substantial or undesirable build-up of contaminants in the hot water circuit or any back-leaching of those contaminants into the cold water circuit  30 . 
     The produced pure water  14  flows from the control valve  114  to a post-treatment final catalyst filter cartridge  160  shown (in one preferred form) mounted on the fixed manifold  74  adjacent the control valve  114  ( FIGS. 1,4-6, 8-9 and 11 ). This post-treatment cartridge  160 , as shown best in  FIG. 11 , includes an inflow port  162  for pure water inflow from the control valve outlet port  120  and further through a flow path  161  in the fixed manifold  74 , to a position between a lower catalyst filter element  164  and an upper carbon-type filter element  166 . Assuming that the pure water dispense faucet  20  is in a normally closed position, the pure water flow passes downwardly through the lower catalyst filter element  164  and further through a flow port  168  and further through a manifold flow path  169  ( FIG. 9 ) and a flow conduit  170  to the pure water storage reservoir  38 . In the preferred form, the catalyst filter element  164  defines a filtration chamber  172  filled partially (preferably less than ½ the chamber volume) with a particulate catalyst media or agent  173  including zinc, such as the same copper-zinc catalyst material used in the prior-described catalyst pre-filter  16 . A portion of the catalyst zinc will be dissolved into the pure water flow passing therethrough, for purposes of maintaining water and storage tank freshness. 
     The pure water storage reservoir  38  includes a lower water storage chamber  174  ( FIGS. 1 and 11 ) separated from an upper closed air-filled pressure chamber  176  by a resilient diaphragm or bladder  178 . As the pure water storage chamber  174  fills with the purified water  14 , the bladder  178  deforms to reduce the volumetric size of the pressure chamber  176 . As the pure water chamber  174  reaches a substantially filled condition, the pressure applied to the pure water chamber  174  by the air-filled pressure chamber  176  increases slowly to a maximum predetermined pressure level. When this maximum pressure level is reached, as denoted by a ratio between the downwardly exposed area of a diaphragm valve  180  at the lower end of the valve spool  124  ( FIG. 10 ) on the control valve  114 , versus the upwardly exposed area of the seal stop  122  at the upper end of the valve spool  124 , the spool shifts upwardly within the control valve housing  116  to close the pure water inflow port  118  and thereby halt pure water production. In a typical RO system, these surface areas are designed to achieve closure of the seal stop  122 , to halt pure water production, when the pressure within the pure water chamber  174  reaches about ⅔ the tap water line pressure. 
     As previously described, cessation of pure water production is accompanied by re-routing of the brine flow through the recycle conduit  40  from the hot water circuit  34  (during pure water production), and instead coupling the now-untreated water flow passing from the RO membrane and through the second RO outlet path  108  through the recirculation conduit  158  to the catalyst pre-filter  16 , as by coupling to the catalyst pre-filter via an inlet fitting  183  ( FIGS. 1, 2 and 2   a ) or the like. That is, when pure water production is halted, tap water is continuously recirculated through the catalyst pre-filter  16 , the pre-membrane filter  64 , and the RO membrane  12 , in lieu of continuously cycling this flow to the hot water system. As a result, and in view of the fact that pure water production is normally halted for a substantial period of time each twenty-four hour period, the filtration load represented by untreated tap water is removed from these system components whenever pure water production is halted. Instead, these system components are subjected only to prior-treated water thereby further extending the operating service life thereof. 
     When pure water  14  is dispensed upon opening of the pure water dispense faucet  20 , the pressure within the pure water chamber  174  of the storage reservoir  38  falls. When this occurs, the applied pressure to the diaphragm valve  180  at the lower end of the valve spool  124  ( FIG. 10 ) drops, thereby opening the pure water inlet port  118  and permitting resumed production of purified water by the RO cartridge  12 . Resumed pure water production is accompanied, of course, by re-directing the now-brine outflow from the second RO outlet path  108  from the catalyst pre-filter  16  back to the hot water circuit  34  via the recirculation conduit  40 . 
     During dispensing, the pure water  14  back-flows from the storage reservoir  38  through the conduit  170  for passage back into contact with the catalyst media  173  within the final catalyst filter cartridge  160 . In this regard, as shown best in  FIG. 11 , the pure water  14  up-flows through the particulate bed of the catalyst media  173 , resulting in stirring and fluidizing of the media  173  sufficient to turbulently abrade and refresh the media  173  in the same manner as previously described with respect to the catalyst pre-filter  16 . From the catalyst filter element  164 , the pure water  14  combines with newly produced pure water  14  for flow together through the overlying carbon-based filter element  166  before discharge through an outflow port  182  and associated flow conduit  184  to the faucet  20  for dispensing. 
     When the pure water dispense faucet  20  is turned off, pure water dispensing is halted. But, pure water production will continue until the pure water chamber  174  of the storage reservoir  38  substantially re-fills. At that time, the pressure within the pure water chamber  174  rises sufficiently to shift the spool valve  124  back to a closed position halting pure water production, as previously described. 
       FIGS. 12-14  show the pure water dispense faucet  20  in more detail, in accordance with one preferred form of the invention. As shown, the pure water dispense faucet comprises a compact faucet body  186  having a threaded lower end adapted for conventional mounting through a sink-type countertop  21  ( FIGS. 12 and 14 ) or the like. This faucet body  186  includes an upper portion  188  normally positioned above the countertop. The faucet body  186  further defines an internal flow path  190  coupling the pure water dispense conduit  184  through a manually operable faucet valve  192 , operated by a rotatably mounted faucet handle  193 , to an upwardly projecting dispense spout  194  of typically inverted, generally U-shaped configuration. 
     The upper portion  188  of the dispense faucet body  186  carries a plurality of indicator lights, such as the illustrative pair of vertically opposed lights  196  of common color (such as green or blue), and a third indicator light  198  of a different color (such as yellow or red). These indicator lights  196 ,  198  are shown best in  FIGS. 13-14 , and may comprise relatively low power LED-type lights provided to indicate water quality in response to conductivity readings taken regularly during system operation by a water quality monitor circuit  200 , as depicted schematically in  FIG. 15 . This monitor circuit  200  is preferably incorporated into the faucet assembly, preferably on a circuit board  201  ( FIG. 1   2 ) carrying the LED&#39;s  196 ,  198 . Alternately, if desired, the monitor circuit  200  can be installed at any other convenient location such as on or within the manifold housing  62  located beneath the countertop  21 . The monitor circuit  200  is powered by a suitable power source (not shown) such as a battery or a standard alternating current power supply. 
     More particularly, and in accordance with one preferred form of the invention, the monitor circuit  200  is coupled to and operates a pair of electrodes  202  and  204  for respectively taking conductivity readings of the untreated tap water inflow and the produced purified water  14 . In this regard, these electrodes  202 , 204  may be located at a variety of convenient positions along the various water flow paths in the purification system. Persons skilled in the art will understand that such conductivity readings are reflective of the presence of dissolved solids in the monitored water supplies, whereby a comparison between the conductivity of the untreated tap water versus the produced purified water represents an indication of the performance efficiency of the RO membrane. When the detected conductivity ratio indicates inadequate purification of the water, it is time to replace the RO cartridge  12 . Such replacement, in the system disclosed herein, is anticipated on an infrequent basis, i.e., at about 5-7 year intervals. 
     The monitor circuit  200  is programmed to take conductivity readings following a predetermined time delay (such as about 5 minutes) after opening of the control valve  14  to initiate pure water production, and thereafter repeat such conductivity readings according to a programmed schedule (such as about every 5 minutes) following the predetermined time delay until the control valve  114  closes to halt pure water production. These conductivity readings are stored in a circuit memory  206  ( FIG. 1   5 ). In the event that a predetermined consecutive number of conductivity readings (such as 5 consecutive readings) indicates poor water quality during any single pure water production cycle, i.e., that the RO cartridge  12  needs to be replaced, the monitor circuit  200  illuminates the yellow or red indicator light  198  in a continuous or continuously blinking fashion until RO cartridge replacement. In an alternative preferred form, the monitor circuit  200  is programmed for illuminating the lights  196  and  198  in an alternating blinking sequence until RO cartridge replacement. In the absence of the predetermined consecutive number of unsatisfactory readings during any single pure water production cycle, the monitor circuit  200  is programmed to automatically re-set upon closure of the control valve  114 . The circuit  200  is also programmed to re-set in the event that the pure water production cycle is halted before the predetermined number of consecutive readings can be taken. 
     Otherwise, the monitor circuit  200  is programmed to illuminate the green or blue indicator lights  196  each time the pure water dispense faucet  20  is turned on to dispense water, as by response to a flow switch or the like (shown in  FIG. 15  in the form of a flow meter  610 , as will be described in more detail). As shown best in  FIG. 13 , an outer shroud  208  mounted about the upper portion  188  of the faucet body  186  carries a partially transparent or translucent brand name logo element  210  with raised logo elements shaped to fit snugly within a logo cutout  211  formed in the outer shroud  208 . If desired, a clear or transparent seal such silicon putty (not shown) may be used to prevent accumulation of dirt and the like within small crevices between the cutout  211  and the raised logo on component  210 . The color of the illuminated indicator lights  196  or  198  backlight and are thus visible externally via this transparent or translucent logo element  210 . Alternately, if desired, the transparent or translucent logo element  210  may be positioned in front of the green or blue indicator lights  196 , with a separate port  212  ( FIG. 13 ) of the like positioned in front of the yellow or green indicator light  198 . 
     In accordance with a further aspect of the invention, the upper portion  188  of the dispense faucet body  186  may additionally carry a photocell  214  ( FIG. 14 ) for detecting the level of ambient light. The photocell  214  is integrated into the monitor circuit  200  ( FIG. 1   5 ) for illuminating one or both of the indicator lights  196 , or a different indicator light (not shown), when the ambient light level falls. Accordingly, the photocell  214  effectively causes indicator light energization to provide a night-light function. In the preferred form, the circuit  200  ( FIG. 15 ) responds to the photocell  214  to illuminate only one of the two indicator lights  196 , or to illuminate both lights  196  at a reduced power level, thereby providing a relatively dim yet effective night-light function. 
     When the monitor circuit  200  illuminates the indicator light  198  to indicate unsatisfactory RO system performance, it is necessary to replace the RO cartridge  12 . This is accomplished by removal and replacement of the multi-cartridge unit  36 . In this regard, illumination of the indicator light  198  requires a replacement multi-cartridge unit  36  to be ordered and received. As previously shown and described herein, the slide-out drawer  80  is opened to accommodate quick and easy lift-out removal of the old multi-cartridge unit  36 , followed by similarly quick and easy drop-in installation of the replacement unit  36  and re-closure of the drawer  80  ( FIGS. 4-6 ). Such removal and replacement of the multi-cartridge unit  36  does not require service personnel to visit the purification system site. 
     In addition, the dispense faucet  20  may carry or otherwise be associated with a flow meter  610  (shown schematically in  FIG. 15 ) for monitoring the total amount of purified water dispensed by the faucet  20  over a period of time. This flow meter  610  is adapted to generate a signal each time the faucet  20  is opened to dispense purified water, wherein this signal is proportional to the water flow rate. Accordingly, the flow meter  610  also functions as a flow switch, in the preferred form, for signaling the monitor circuit  200  to energize the lights  196  each time the faucet  20  is opened to dispense water. This flow rate signal is coupled to the monitor circuit  200  ( FIG. 1   5 ) which responds thereto by maintaining in memory a record indicative of the total or cumulative volume or gallonage of water dispensed. Over a period of time, when the total water volume dispensed equals or exceeds the capacity of the carbon-based system filter elements to remove contaminants from the processed water, the monitor circuit  200  is programmed to provide an indication that the multi-cartridge unit  36  needs to be changed. Such indication may be similar to the indication provided when the conductivity readings (as described above) indicate unsatisfactory RO membrane performance, i.e., the monitor circuit  200  may energize the indicator light  198  to indicate a need to replace the multi-cartridge unit  36 . 
     While the flow meter  610  may take various forms, one preferred flow meter construction corresponds generally with the flow meters marketed by Blue-White Industries, Ltd., of Huntington Beach, Calif. under the model designations F-440 series. Such flow meters generally comprise a core float member formed from a magnetic-type stainless steel or the like captured within a tapered housing disposed in-line with the dispense faucet flow path  190  ( FIG. 1   2 ) for displacement along said tapered housing by an increment proportional to the water flow rate therethrough. By surrounding such flow meter  610  with a conductive coil  612  ( FIG. 1   5 ), an electric signal is generated proportional to the water flow rate, wherein this proportional electric signal is coupled to the monitor circuit  200 . In this arrangement, it is desirable to position the monitor circuit  200  relatively close to the flow meter  610 , as by incorporating the monitor circuit  200  within the faucet assembly on the circuit board  201  ( FIG. 12 ), to facilitate accurate flow meter calibration and operation. Persons skilled in the art will appreciate that alternative flow meter constructions may be used. 
     To insure proper re-setting of the monitor circuit  200  following replacement of the multi-cartridge unit  36 , each unit  36  is provided with a unique marking or other suitable identification means such as a unique bar code label  216  or the like ( FIGS. 6 and 15 ). This label  216  is positioned to be scanned optically by an optical reader  218  ( FIG. 1   5 ), such as a bar code reader, mounted on or near the internal base  76  of the manifold housing  62 . This reader  218  is connected to a re-set portion of the monitor circuit  200  which includes in its memory the unique code associated with the prior multi-cartridge unit  36  stored previously therein. In the event that the prior multi-cartridge unit  36  is simply removed from and then re-installed into the slide drawer  80 , the reader  218  will read and recognize the same code and thereby not function to re-set the monitor circuit  200 . Instead, the reader  218  requires a new and different code to be scanned, in order to re-set the monitor circuit  200 . Upon such re-set, the monitor circuit  200  is programmed to retain the new cartridge code  216  in its memory, pending subsequent removal of the newly installed cartridge for replacement by still another multi-cartridge unit having still another different code  216 . 
     Persons skilled in the art will appreciate that alternative identification means and associated reader means may be employed, including but not limited to radio frequency identification devices (RFID) and the like. Persons skilled in the art will also recognize that the unique code  216  associated with a newly installed or replacement multi-cartridge unit  36  may also include means for re-programming the monitor circuit, e.g., as by modifying the cumulative dispensed gallonage required to signal that it is time to replace the unit  36 . In this manner, the monitor circuit  200  can be reprogrammed as needed to accommodate local water supply conditions, new technology developments, and the like—all without requiring direct user intervention and/or any on-site visits by service technicians. 
     In accordance with a further aspect of the invention, the pure water dispense faucet  20  is adapted for receiving and distributing a flow of filtered or purified air into the room in which the faucet  20  is located. In this regard, the shroud  208  on the upper portion  188  of the faucet body  186  includes an array of vent ports  220  ( FIGS. 12-13 ) coupled to an air flow conduit  222  ( FIG. 1   2 ) passing upwardly through the faucet body  186 . This air flow conduit  222  has an upstream end coupled to a fan  224  ( FIGS. 1 and 8 ) mounted on or near the internal base  76  of the manifold housing  62 . The fan  224  draws ambient air from a small plenum box  226  which is linked in turn to a downstream end of a filter chamber  228  ( FIG. 8 ) having an air filter element  230  mounted therein. This filter chamber  228  occupies a substantial portion of a hollow internal volume of the fixed manifold base  76 , and communicates with at least one air inflow port  232 . A hinged door  234  or the like at the front of the internal base  76 , below the slide-out drawer  80 , permits access to the air filter chamber  228  for removal and replacement of the filter element  230  on a periodic or as-needed basis. 
       FIG. 16  shows a modified control valve  314  constructed in accordance with an alternative preferred form of the invention, for use in lieu of the control valve  114  shown in  FIG. 10 , and wherein components corresponding in structure or function with those shown and described in connection with the control valve  114  are identified by common reference numerals increased by 200. As shown, the modified control valve  314  includes an elongated valve body or housing  316  defining a pure water inlet port  318  and a pure water outlet port  320  at opposed ends thereof. An elongated valve spool  324  extends generally between these inlet and outlet ports  318 ,  320 , with a seal stop  322  movable relative to an associated seat  326  for opening to permit pure water production, and for closing to halt pure water production. A spring  334  biases the valve spool  324  toward a normal position halting pure water production. 
     The modified control valve  314  defines a central control chamber  236  coupled via a fitting  237  to the tap water supply, as by means of a flow conduit  238  or the like. A control valve  240  on the valve spool  324  responds to the water pressure within the control chamber  236  for applying a downward force to the valve spool  324 . This downward force via the control valve  240  cooperates with backpressure applied to a lower diaphragm valve  380  to regulate opening and closing movement of the valve spool  324 . Again, in a preferred arrangement, the seal stop  322  is designed to close when the pressure within a pure water storage reservoir  38  is about ⅔ the tap water line pressure. 
     The valve spool  324  is adapted to operate a switch  242 , such as a conventional magnetically actuated reed-type switch, for controlling operation of the pump  136  used to recycle the brine flow to the hot water circuit  34 . In this regard, the valve spool  324  may carry a magnetic element  241  in operative association with a reed-type switch  242 . When pure water production is started, upon opening of the control valve  314 , the switch  242  activates the pump  136  for recycling the brine to the hot water system  34 , as previously described. When the control valve  314  closes, the pump  136  is de-activated and water is not recirculated through the RO membrane. Instead, the modified control valve  314  halts water circulation to and through the RO cartridge. 
       FIG. 17  shows a further modified control valve  514  constructed in accordance with a further modified preferred form of the invention. As shown, the control valve  514  has a simplified construction wherein flow ports and the like through moving diaphragm components are not required. 
     More particularly, the modified control valve  514  includes a multi-segmented valve body  550  having a first pressure port  552  coupled to receive produced purified water from the flow line  109  to a lower chamber  554  containing a valve head  556  normally biased by a spring  558  into sealed engagement with a valve seat  560 . The valve seat  560  defines a short flow passage leading from the lower chamber  554  to a lower control chamber  562  which in turn communicates with a second pressure port  564  coupled for pure water flow to the storage reservoir  38  (as previously shown and described herein). One wall of the lower control chamber  562  is defined by a resilient diaphragm  566  carried at a lower end of a rigid member  568 . A second and somewhat smaller-area resilient diaphragm  570  is carried at an upper end of this rigid member  568  and defines one wall of an upper control chamber  572  in flow communication with a third pressure port  574  coupled with the tap water inflow line  238 . 
     The rigid valve member  568  carrying the lower and upper diaphragms  566 ,  570  of differential area size is designed to operate the switch  242  used to turn the pump  136  off and on in response to the filled or unfilled state of the pure water storage reservoir  38 , as previously shown and described with respect to  FIG. 16 . In one form, the member  568  may comprise a magnetic element used to operate a reed-type switch  242  as described in  FIG. 16 . In another preferred form, the member  568  may incorporate a laterally open port  576  associated with an emitter  578  and a detector  580  mounted on the housing  550  at opposite ends of the port  576 . This emitter-detector combination  578 ,  580  is coupled to the monitor circuit  200  ( FIG. 1   5 ) for response to shifting displacement of the member  568  to turn the pump  136  on and off. 
     More particularly, when the pure water storage reservoir reaches a substantially filled condition, the hydraulic pressure rises in the storage reservoir  38  to increase the pressure along the line  170  and within the lower control chamber  562  applied to the lower diaphragm  566 . This hydraulic pressure combines with the force applied by the spring  558  to overcome the downward force attributable to the tap water pressure within the upper control chamber  572 , thereby shifting the valve head  556  to a closed position against the valve seat  560 , and further thereby halting further pure water flow through the control valve  514  to the reservoir  38 . At the same time, an upwardly protruding pin  557  on the valve head  556  engages a support plate  582  mounted centrally on the lower diaphragm  566  to shift the rigid valve member  568  upwardly to move the transverse port  576  into alignment with the emitter-detector combination  578 ,  580 . When such alignment occurs, the monitor circuit  200  is signaled to turn the pump  136  off. Thereafter, upon dispensing of sufficient pure water from the reservoir  38 , the hydraulic pressure applied to the lower control chamber  562  is sufficiently reduced (relative to the tap water pressure within the upper control chamber  572 ) to cause the rigid valve member  568  to shift downwardly in a manner to re-open the valve head  556  to permit resumed pure water production. Such downward shifting of the rigid valve member  568  is accompanied by misalignment of the emitter-detector combination  578 ,  580  with the transverse port  576 , thereby signaling the monitor circuit  200  to re-activate the pump  136 . 
     In accordance with a further aspect of the invention, and as shown by way of example in  FIG. 17 , the system may further include a remote means for disabling pure water production in the event that the user (i.e., a homeowner or business customer) fails to maintain a current or paid-up account with the system vendor. In this regard,  FIG. 17  shows an antenna  590  carried by a telephonic reception device  592 , such as a conventional beeper device, linked to a disable valve  594  such as a latching solenoid valve incorporated into the system plumbing lines, such as along the flow path  170  for pure water flow to the reservoir  38 . In the event that the customer fails to maintain current account payments, the vendor can remotely signal the reception device  592  to operate the disable valve  594 , directly or indirectly, by appropriate signaling to the monitor circuit  200 , to close the pure water flow path  170 . Such closure of the disable valve  594  effectively precludes further use of the system by the customer, and provides a clear indication that the customer&#39;s account needs to be brought up to date. Upon receipt of an appropriate payment, the vendor can remotely reactivate the system by signaling the reception device  592  to re-open the disable valve  594 . In this regard, each system reception device  592  is associated with a unique telephonic address or code. 
     When the disable valve  594  is closed, the monitor circuit  200  may be programmed to respond by illuminating the light  198  for further providing the customer with a clear indication that the system  10  is not functioning properly. Upon remote re-signaling to re-start the system, the light  196  on the faucet valve  192  can be illuminated, as by blinking for a predetermined number of cycles, to indicate to the customer that system operation has been reactivated. In addition, during normal operation, the memory circuit  200  can be programmed to deliver “open” signals to the disable valve  594  at repeated intervals to safeguard against undesired or unexpected system shut-down due to valve closure. The disable valve  594  comprises, in the preferred form, a normally closed valve whereby the valve  594  automatically closes upon an interruption of the household power supply, but is automatically re-opened by the regular “open” signals upon resumption of the household power supply. 
     While the remote disabling means is shown and described for use with the modified control valve  514  shown in  FIG. 17 , persons skilled in the art will appreciate that the remote disabling means may be employed in any or all embodiments of the invention disclosed herein. 
       FIGS. 1   8 - 1   9  illustrate a modified reverse osmosis cartridge  412 , wherein the modified RO cartridge  412  can be used in lieu of the RO cartridge  12  depicted in  FIGS. 1,4-6, and 8-9 . This modified RO cartridge  412  provides a relatively simple yet effective means for injecting or adding one or more selected minerals in dissolved form, such as calcium and/or magnesium and others, to the produced purified water. 
     As shown in  FIG. 18 , the flow path  103  provides tap or cold water inflow to the modified RO cartridge  412 , in the same manner as previously shown and described herein. An RO membrane assembly  414  and related cartridge housing components are modified to accommodate mineral addition to the produced purified water. More particularly, the RO membrane assembly  414  (shown best in  FIG. 19  in partially exploded form) comprises a conventional multiply wrap of a semi-permeable membrane material  416  in combination with intervening plies of a porous wick material  418 . These plies  416 , 418  are wrapped about a central support tube  420  ( FIG. 1   8 ), and the resultant subassembly is fitted in turn within a hollow cartridge housing  422 . As is known in the art, the opposite ends (upper and lower, in  FIGS. 18 and 19 ) of the semi-permeable membrane material  416  include impermeable welds  424 . The modified RO membrane assembly  414  additionally includes an intermediate weld  426  disposed in spaced relation with the upper weld  424 . Accordingly, the intermediate weld  426  cooperates with the lower and upper welds  424  to subdivide the semi-permeable membrane material  416  into a first or lower filtration region  428  and a second or upper filtration region  430 . 
     The tap or cold water inflow is flow-coupled via the flow path  103  to a lower end of the wrapped plies  416 ,  418  ( FIG. 18 ). This water inflow passes along the wick material  418  between the lower end weld  424  to communicate with the first or lower filtration region  428 . As is known in the art, the semi-permeable membrane material constituting this first filtration region  428  converts the water inflow into relatively purified water communicated radially with the pure water outlet path  106 , and a brine flow communicated axially with the brine outlet path  108 . In the modified RO cartridge  412 , a portion of the water inflow proceeds further upwardly along the wick material  418  past the intermediate weld  426  to the second or upper filtration region  430  which produces an additional or secondary pure water flow. In the preferred configuration, the membrane surface area defined by the second filtration region  430  is considerably less than the membrane surface area defined by the first or primary filtration region  428 . 
     As viewed in  FIG. 18 , the purified water produced by the primary filtration region  428  flows through a check valve  432 , such as a duckbill-type check valve, to the pure water outflow line  106 . By contrast, the purified water produced by the upper or secondary filtration region  430  passes through a small check valve  434  (such as a duckbill-type valve) into the hollow interior of the central support tube  420  which is filled at least partially with one or more water soluble mineral agents  436 , such as calcium and/or magnesium in particulate form. This smaller flow of produced purified water thus dissolves and entrains the mineral agents  436  for outflow via another check valve  438  (such as a duckbill-type valve) to the pure water outlet flow path  106 . 
     Accordingly, during pure water production, the modified RO cartridge  412  provides a means for injecting one or more desirable mineral agents into the purified water produced by the system. When pure water production is halted, such as when the associated pure water storage reservoir reaches a substantially filled condition (as previously shown and described herein), the check valves  434  and  438  at opposite ends of the mineral-containing chamber are closed to correspondingly halt the mineral injection process. 
       FIG. 20  depicts still another alternative preferred form for a control valve  714 , wherein this modified control valve  714  includes redundant closure mechanisms to positively insure cessation of water flow through the Ro cartridge  12  when the pure water reservoir  38  reaches a substantially filled condition. 
     More particularly, the modified control valve  714  includes a multi-segmented valve body  750  having a first pressure port  752  coupled to receive produced purified water from the flow line  109  to a lower inlet chamber  754 . A valve head  756  is positioned within this lower inlet chamber  754  and is normally biased by a spring  758  in an upward direction toward sealed engagement with an overlying valve seat  760 . The valve head  756  is carried centrally by a resilient diaphragm  757  having a peripheral array of flow ports  759  formed therein. 
     The valve seat  760  defines a short flow passage leading from the lower inlet chamber  754  upwardly into a lower control chamber  762  which in turn communicates via a tapered valve seat port or bore  763  with an overlying secondary chamber  764  coupled via a second pressure port  765  with the flow line  170  for pure water flow to the storage reservoir  38  (as previously shown and described herein). One wall of this secondary chamber  764  is defined by a resilient diaphragm  766  carried at a lower end of a rigid valve poppet member  768 . A second and somewhat smaller-area resilient diaphragm  770  is carried at an upper end of this rigid valve poppet member  768  and defines one wall of an upper control chamber  772  in flow communication with a third pressure port  774  coupled with the tap water inflow line  238 . 
     The rigid valve poppet member  768  carrying the lower and upper diaphragms  766 ,  770  of differential area size is designed to operate a switch (not shown) used to turn the pump  136  on and off in response to the filled state of the pure water storage reservoir  38 , as previously shown and described with respect to  FIGS. 16 and 17 . In addition, the valve poppet member  768  comprises or carries a magnet element  769  which attracts and retains a metal (stainless steel, or the like) keeper plate  782  on the underside of the lower, larger diaphragm  766 . A valve stem  784  projects downwardly from the keeper plate  782  through the secondary chamber  764  and further through the tapered valve seat port  763  and the lower control chamber  762  for bearing engagement with an upper side of the valve head  756 . 
     In normal operation, during pure water production, the pressure differential across the rigid valve poppet member  768  is sufficient to shift the poppet member  768  in a downward direction so that the valve stem  784  engages and opens the lower valve head  756  against the closure force applied by the biasing spring  758 . In this mode, the open valve head  756  permits produced purified water from the RO cartridge  12  to flow through the ports  759  in the lower diaphragm, and further through the valve seat  760  and the two chambers  762 ,  764  to the pure water reservoir  38 . 
     When the pure water reservoir  38  reaches a substantially filled condition, the pressure differential across the valve poppet member  768  causes upward shifting thereof with the valve stem  784 . As the valve stem  784  displaces upwardly, a seal ring  790  thereon is moved into and sealingly engages the tapered valve seat or bore  763  separating the two chambers  762 ,  764 . In a preferred form, this seal ring  790  has a quad or substantially I-beam cross sectional configuration as shown, to provide redundant axially spaced upper primary and lower secondary seal interfaces with the bore  763 . Upon upward closure movement of the popper member  768  and associated valve stem  784 , the upper primary seal initially displaces into the tapered bore  763  for sealing engagement therewith. Upon sealing, further upward displacement of the valve stem  784  is halted. If sealing is incomplete, the valve stem  784  displaces further upwardly within the tapered bore  763  (as shown in  FIG. 20 ) so that the lower secondary seal on the seal ring  790  is also moved into sealing engagement therewith for positive valve closure. Alternately, if desired, other redundant seal ring configurations, such as duplicate 0-rings or the like defining multiple or redundant seal interfaces may be used. In any event, such upward stem displacement is also accompanied by separation of the valve stem lower end from the valve head  756 , whereby the biasing spring  758  now acts to positively displace the valve head  756  to a position closed on the associated seat  760 . Thus, pure water flow through the RO membrane is positively halted with redundant seals provided by the valve head  756  and the seal ring  790  (which itself provides redundant diametric seals within the bore  763  carried by the common valve stem  784 ). When such sealing occurs, the pressure differential across the RO membrane is substantially eliminated, i.e., the pressure within the lower inlet chamber  754  slowly rises substantially to the tap water inflow pressure at the upper control chamber  772 , thereby assisting in positive control valve closure. Persons skilled in the art will appreciate that the valve head  756  may be omitted, if desired. 
     When pure water is dispensed from the reservoir  38 , the pressure level within the chamber  764  drops. After a sufficient volume of pure water is dispensed, such as several glass-type servings, the pressure falls sufficiently to shift the valve poppet member  768  downwardly for re-opening the valve head  756  and the seal ring  790  for resumed pure water production. 
       FIGS. 21-24  depict a modified manifold housing, which corresponds generally in structure and functional operation with the manifold housing  62  shown and described previously herein with respect to  FIGS. 3-6 . For convenience and consistency of description, components shown in  FIGS. 21-24  are identified by reference numerals common to those used in  FIGS. 3-6 , increased in value by  800 . Accordingly, the modified manifold housing  862  generally comprises a manifold base  868  and associated cover  881  for slidably receiving and supporting a multi-cartridge unit  36  (not shown in  FIGS. 21-24 ) in flow-coupled relation with related system components (as previously shown and described, e.g., with respect to  FIGS. 1 and 4-9 ). The multi-cartridge unit is removably carried on a slide-out drawer  880  having a front panel  884  carried thereby for normally closing the manifold housing  862  when the multi-cartridge unit is operationally installed. 
     The modified manifold housing  862  of  FIGS. 21-24  includes an improved latch mechanism  802  for releasably retaining the front panel  884  in a normally fully closed position, with the multi-cartridge unit  36  therein properly and operationally coupled with related system components, and without risk of water leakage therebetween. This improved latch mechanism  802  is designed for secure, substantially fail-safe retention in the closed position, but can be opened quickly and easily when desired. 
     More particularly, the latch mechanism  802  includes a pair of magnets  804  and  806  carried respectively by the manifold base  868  and the front panel  884  for normal positioning in close proximity with each other, when the front panel  884  is in a fully closed position as viewed in  FIG. 22 . Importantly, in this fully closed position, the two magnets  804 ,  806  are oriented with their respective opposed magnetic poles (North and South) aligned so that the two magnets  804 ,  806  strongly attract each other to retain the front panel  884  in the fully closed position.  FIG. 22  shows the base-mounted magnet  804  oriented with its South pole overlying the related North pole, and the panel-mounted magnet  806  oriented with its poles in a reverse configuration in respective alignment with the poles of the base-mounted magnet  804 . The size and strength of these magnets  804 ,  806  are chosen to provide a sufficiently strong magnetic attraction force so that, as the front panel  884  is displaced toward the closed position, the magnets attract each other with a sufficient force to insure full panel/drawer closer with the multi-cartridge unit  36  fully and properly seated and engaged with the associated ports on the fixed manifold  74  (as viewed previously with respect to  FIG. 7 ). In other words, the magnetic attraction is sufficiently strong to overcome any hydraulic line pressure at the inter-fitted ports, wherein such line pressure might otherwise preclude full engagement and result in water leakage at these connection sites. 
     The front panel  884  and associated slide-out drawer  880  can be quickly shifted quickly and easily to the open position for access to and replacement of the multi-cartridge unit, when and if desired. The panel-mounted magnet  806  is carried at a lower end of a vertically reciprocal slide bar  808  mounted at an inboard side of the front panel  884 . This slide bar is slidably guided along a track  810 , and has an upper end thereof pivotally coupled via one or more crank links  812  ( FIG. 24 ) to a movable drawer pull  886 . As shown, this drawer pull  886  is normally positioned in a “down” orientation disposed substantially within a recessed pocket  814  formed on an outboard face of the front panel  884 , to correspondingly position the panel-mounted magnet  806  in an attraction orientation relative to the base-mounted magnet  804 . The drawer pull  886  can be lifted through a short stroke ( FIGS. 21 and 23-24 ) to lift the slide bar  808  and the panel-mounted magnet  806  sufficiently to shift the inter-magnet pole alignment to a repulsion orientation. That is, as viewed best in  FIG. 23 , the panel-mounted magnet  806  is lifted sufficiently to align its lower South pole with the upper South pole on the base-mounted magnet  804 , resulting in a strong repulsion force which quickly and easily shifts the front panel  884  (and the slide-out drawer  880  coupled thereto) to a partially open position ( FIGS. 21 and 23-24 ) with the multi-cartridge unit disengaged from the internally disposed fixed manifold  74  ( FIG. 7 ). The thus-disengaged components permit further and easy manual slide-out displacement of the front panel  884  and drawer  880  to a fully open position for access to the multi-cartridge unit. 
     Thereafter, return slide-in displacement of the front panel  884  and associated drawer  880  is accompanied by return alignment of the magnets  804 ,  806  in the attraction orientation. That is, with the drawer pull  886  manually released, the panel-mounted magnet  806  falls by gravity back to the attraction orientation. As the panel-mounted magnet  806  approaches the base-mounted magnet  804  (upon drawer closure), the attraction force strongly pulls and retains the front panel  884  and associated drawer  880  to the fully and securely closed position. Conveniently, at this fully closed position is reached, downwardly protruding tabs  816  ( FIG. 24 ) at a lower end of the slide bar  808  guide into and seat within upwardly open cut-outs or pockets  818  formed in the base  868  for further positive mechanical retention of the drawer  880  in the fully closed position. These tabs  816  are sized for pull-out disengagement from the associated pockets  818 , when the drawer pull  886  is lifted (as previously described) for shifting the panel-mounted magnet  806  to the repulsion position. 
     Alternative combined magnetic and mechanical closure arrangements will be apparent to those persons skilled in the art. 
     In a further embodiment of the invention, a power indicator light  902  may be carried on the manifold housing  862  as viewed in  FIG. 21 , for indicating that the reverse osmosis system is in a power-on state. In addition, a water quality light  904  may also be provided for indicating the state of water purity, wherein this light  904  is adapted for illumination at one color (such as blue or green) when the water quality is acceptable, and at a second color (such as yellow or red) when the water quality is not acceptable. In this regard, the water quality light  904  is, in a preferred form, provided in addition to the water quality lights  196 ,  198  as previously shown and described herein. 
     In addition, the manifold housing  862  may further carry a bank of purification life lights  906 , such as the bank of four lights shown in  FIG. 21 . These purification life lights  906  provide an indication of the remaining estimated life of the multi-cartridge unit, based on total dispensed pure water outflow as measured by the flow meter  610  ( FIG. 1   5 ). In a preferred form, the flow meter  610  is coupled via the monitor circuit  200  and associated memory  206  to the lights  906  to illuminate one or more of said lights  906  based on the estimated remaining life of the multi-cartridge unit. 
     In accordance with a still further aspect of the invention, the monitor circuit  200  ( FIG. 1   5 ) may be programmed to energize the lights  196 ,  198  in a controlled manner, in response to predetermined user-initiated activity, for purposes of verifying that the system  10  continues to produce purified water of acceptable quality. In this regard, the system  10  is designed for relatively prolonged operation without requiring replacement of the RO cartridge  12  or other system components, whereby some users may begin to question whether the continued illumination of the light or lights  196  indicating acceptable water quality is in fact correct. To verify proper operation, the monitor circuit  200  may be preprogrammed for such verification, in response to a predetermined user-initiated action, such as turning the dispense faucet  20  on and off in a rapid sequence at least  3  times within a short time interval such as within about 10 seconds. When this activity is detected by the monitor circuit  200 , by virtue of the flow signals provided by the flow meter  610  or the like, the monitor circuit  200  will controllably illuminate the lights  196  and  198 , such as in an alternating blinking mode, for a predetermined number of times (such as 5), and then illuminate the light  196  or the light  198  associated with the most recent conductivity reading which is retained in the memory  206  of the monitor circuit  200 . Such user-initiated verification of proper system operation may occur in response to a user-initiated telephone inquiry, and/or outlined in a system owner&#39;s manual. 
     A variety of further modifications and improvements in and to the improved reverse osmosis water purification system  10  of the present invention will be apparent to persons skilled in the art. By way of limited example, it will be appreciated that the components of the system  10  may be arranged in different configurations suitable for appropriate component access and service over an extended service life. In this regard, the post-treatment cartridge  160  may be disposed outside the multi-cartridge housing  62 , such as alongside or on top of the catalyst pre-filter  16 . In addition, if desired, the pump  136  may be mounted inside the multi-cartridge housing  62 . Accordingly, no limitation on the invention is intended by way of the foregoing description and accompanying drawings, except as set forth in the appended claims.