Abstract:
An apparatus and corresponding method for purifying water is described. The apparatus includes a supporting housing, a source of power, a filter device containing at least one interchangeable filter unit having one or more filter elements, a mechanism for driving water through the filter device and a timing mechanism for monitoring elapsed time of operation and a mechanism for monitoring cumulative volume of water having flowed through the filter device which are each coupled to a filter memory. The mechanism for driving water through the filter device includes a cylinder holder on which an interchangeable gas pressure cylinder can be mounted, a gas release mechanism housed in the cylinder holder, a flow regulator and conduits connecting the other components together.

Description:
This application is a continuation of international application number PCT/IL98/00470, filed Sep. 28, 1998. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to apparatus and methods for purifying water that is or may be infected by microorganisms and rendering it potable, particularly for use in localities where the water supply is unsafe or unreliable, and dispensing purified water. In particular, it relates to means for rendering drinking water sterile, and thus safe for infants and other persons that must be protected against even mild infection. In a form of the invention, the apparatus is self-contained, adapted for home use, and can be easily carried and displaced by the user. 
     BACKGROUND OF THE INVENTION 
     In many localities, no safe and reliable water supply is available. A water distribution system may be lacking or, frequently, such a system may exist but deliver water that is not or may not be safe and fit for drinking because it is contaminated, particularly by microorganisms. The problem of providing safe, potable water in such localities, without the addition of chemicals, which impart a bad taste to the water and are not without danger, has received wide attention and has found a variety of solutions in the art. It is known to connect to a water conduit or to a water faucet a purifying apparatus provided with filtering means. For instance, U.S. Pat. No. 5,338,456 discloses a water purification process for removing dissolved solids of a type that are normally present in a municipal water supply or the like, which process uses a forced draft decarbonator, a water degasifier, a product outlet, a water level sensor, and a reverse osmosis unit. 
     These apparatus, however, are cumbersome and expensive and are not suitable for independent, family use. Further, they cannot be used when an adequate, centralized water supply system does not exist. Finally, they do not provide a supply of fresh, potable water at any distance from the water faucets, either within the house and in camping. None of them, further, provides sterile water. 
     Another problem which exists in such apparatus is the inner contamination danger created by the fact that, with the passage of time, the apparatus filters become heavily contaminated with microorganisms which multiply, and thus constitute a health hazard instead of a defense against such a hazard. Contamination may derive from a very small number of microorganisms, even from a single one, since their capacity for multiplication is extremely high. 
     JP 05185070 (Kokai No. 5-185070) notes that in domestic water purifiers the filter module must be replaced when the water that has flown through it has exceeded the allowable absorption capacity of the absorbent inside the module, and that water purifiers are known which are provided with a life meter capable of displaying the time of replacing the filter module. However, the known devices are said to be unreliable because they measure only the time of the water flow and this does not provide a reliable indication due to fluctuations in the water flow rate. Therefore said application proposes a domestic water purifier which comprises a constant flow rate valve, a sensor for detecting start and stop of water flow and generating corresponding signals, and means for measuring an integrated operating time based on said signals and displaying a signal when said integrated time reaches a preset value. The constant flow rate valve has the only purpose of permitting to measure said integrated time accurately, and until said preset value has been reached, the filter is not changed regardless of the volume of water that has flown through it, to which no independent significance is attributed. The application shows various structures of constant flow rate valves, but as to the filter module it shows no structure and states that the invention may utilize various structures of the prior art, nor does it describe a complete apparatus free of the drawbacks of the prior art. 
     It is the purpose of this invention to provide an apparatus for rendering water potable and dispensing potable water, that is free of the limitations and drawbacks of prior art apparatus. 
     It is another purpose of this invention to provide such an apparatus that is adapted to provide sterile water. 
     It is a further purpose of this invention to provide such an apparatus that is self-contained, compact, and economical. 
     It is a still further purpose of this invention to provide such an apparatus that may be portable or not portable, as desired, and, if portable, is easy to carry and displace from one point to another, so that it can be used, for instance, in the home in any room and or outside the home, such as in camping. 
     It is a still further purpose of this invention to provide such an apparatus which is free from the danger of inner contamination, in particular, the danger of the accumulation and multiplication of microorganisms in the apparatus filter. 
     It is a still further purpose of this invention to provide such an apparatus that is simple, easy to use, and safe. 
     It is a still further purpose of this invention to provide such an apparatus in which the ratio of the weight and volume of the apparatus to those of the amount of water that can be dispensed by it are reduced to a minimum. 
     It is a still further purpose of this invention to provide such an apparatus having a filter that is compact and inexpensive and delivers a large volume of purified water per unit filter volume. 
     Other purposes and advantages of this invention will appear as the description proceeds. 
     SUMMARY OF THE INVENTION 
     The apparatus according to the invention is characterized in that it comprises, preferably in addition to a supporting housing and with power means, structural components and interchangeable components, the structural components comprising; 
     1—a cylinder holder, on which a gas pressure cylinder can be mounted; 
     2—a gas dosing mechanism, housed in the cylinder holder; 
     3—an inlet bottle holder, for receiving an unfiltered water bottle; 
     4—a filter base; 
     5—a flow regulator, part of a filter unit or connected to an outlet of the filter unit; 
     6—a dispense water holder, for receiving a filtered water bottle; 
     7—conduit means for successively connecting together the cylinder holder, the inlet bottle holder, the filter base, the flow regulator and the dispense water holder; and 
     8—constant flow and usage controlling devices. 
     and the interchangeable components comprising: 
     8—a gas cylinder; 
     9—an inlet vessel, e.g., a water bottle for receiving the unfiltered water; 
     10—a filter unit housed in the filter base; and 
     11—a vessel for collecting the filtered water. 
     The controlling devices are preferably electronic and more preferably comprise a CPU, means for counting the time passed from a predetermined initial moment, more preferably from the installation of the filter, means for measuring with a desired accuracy the volume of water that has passed through the filter, means for producing and displaying visible signals indicating the conditions of the filter as indicated by the relationship between the counts of said counting means and the reading of said measuring means and a predetermined operating program, and means for preventing the flow of water through the filter when said counts have reached a predetermined threshold value. Said volume measuring means are preferably distinct from and independent of said flow regulator, the purpose of which is not to assist in measuring water volume (though this is not excluded) but to optimize the performance of the filter. More preferably, said volume measuring means comprise means for counting the number of times that an inlet water bottle has been mounted on the apparatus and is operated in or pressurized in the apparatus. 
     The interchangeable gas cylinders contain a gas, typically carbon dioxide, under pressure. The carbon dioxide pressure, in a full cylinder, is generally about 50 atmospheres. Gas under pressure is introduced into the inlet bottle, in such amounts as to generate therein a pressure, considerably lower than that in the gas cylinder, to cause the water to flow through the apparatus, and therefore such bottles, which are generally of plastic, must be of sufficient strength to contain a pressure generally of about 10 atmospheres. 
     The cylinder holder may be any cylinder holder adapted to receive a gas pressure cylinder in a liquid aerating machine, preferably such as described in EP 0 472 995 B1, the content of which is entirely incorporated herein by reference. The liquid aerating machine described in said EP has a gas release mechanism directly controlled by the operator, and this can be used in an apparatus according to the invention. Alternatively, a dosing unit may be provided, that is designed to release a predetermined dose of gas from the gas cylinder every time that a lever or other hand-operated element is actuated. 
     In any case, the cylinder holder has a gas outlet and, preferably, a gas pre-filter is fitted into said gas outlet to prevent any unwanted particles, that may block the subsequent gas passageways, from entering them. This filter will also constitute a security feature, because it will reduce the risk of the liquid carbon dioxide entering the filter. 
     The inlet bottle holder can be fixed or pivoted to the supporting structure, when present, and has means, such as a thread or bayonet, to secure the bottle in position. The bottle holder will comprise a gas inlet, a water outlet, and preferably a gas exhaust valve and a safety valve. Means are desirably provided, as hereinafter better explained, to count the number of unfiltered water bottles of standard volume, for instance, one liter, which are inserted into the apparatus, to determine the overall amount of water that has been purified by it. 
     The water outlet of the inlet bottle holder communicates, by means of a connecting tube or conduit, with the filter base, and the water flows out of the inlet or unfiltered water bottle into said tube or conduit through a dip tube that fits into the said bottle. It is preferred that the dip tube be fitted at its inlet end with a filter to prevent any large particles, that may be present in the unfiltered water, from entering the filter system. 
     The filter base is a support for an interchangeable filter unit and has an inlet and an outlet and means for causing the water to flow through the filter unit. The invention is not limited to any specific type of filter unit, but units comprising filter elements which include depth filter and microporous membrane means, a preferred embodiment whereof will be described hereinafter, are preferred. Further, it is preferred that an ultraviolet (UV) tube of wavelength and intensity sufficient to kill microorganisms and viruses be inserted between the inlet and the outlet of the filter base. 
     The water passes through a flow regulator to assure constancy of flow rate regardless of the pressure that may be exerted by the gas in the gas cylinder and of possible changes in the hydrodynamic resistance of the various components of the apparatus. The flow regulator may be part of the filter, and if not, the filtered water issuing from the filter base passes through it. The flow regulator may be of any known kind. 
     The invention further comprises an apparatus for purifying water, comprising, preferably in combination with a supporting housing and with power means, and unpurified water feed inlet and a purified water dispense outlet, an interchangeable filter having depth filter layers and microporous membrane means interposed between said inlet and said outlet, means for driving the water through the filter at a constant flow rate, means for counting the time passed from the installation of the filter, means for monitoring, with a desired accuracy, the volume of water which has flowed through the filter, and controlling devices for alerting the user when the data acquired by said counting and/or said monitoring means have reached a corresponding threshold values or any one of a plurality of successively increasing, predetermined threshold values, and preferably, means for automatically preventing the flow of water through the filter when the data acquired by said counting and/or said monitoring means have reached the corresponding threshold value or the highest of said plurality of the corresponding threshold values. The means for driving the water through the filter at a constant flow rate may comprise means for applying pressure to the unpurified water and means for controlling the water flow rate regardless of changes of said pressure. 
     The invention further comprises a method for purifying water, comprising: 
     I) providing a first container for unpurified water, a second container for purified water, both containers having the same volume, and filter means; 
     II) applying pressure to the unpurified water; 
     III) driving by said pressure a desired volume of water from said first to said second container while flowing through filter means, preferably through depth filter means and microporous membrane means; 
     IV) maintaining the water flow rate at a constant predetermined value; 
     V) dispensing said desired volume of purified water; 
     VI) repeating the said operations as many times as desired; 
     VII) counting the time passed from the installation of the filter means; 
     VIII) monitoring the volume of water which has flowed through the filter means; and 
     IX) changing the filter means when either said time or said water volume has reached a predetermined threshold value. 
     Preferably, the method comprising automatically preventing the flow of water through the filter means when either said time or said water volume has reached a predetermined threshold value. 
     Further preferably, the method comprises establishing an operating program which includes at least a pair of threshold values one of the time and the other of the water volume, and signaling the condition of the filter, constantly or at predetermined time intervals, to permit the user to know where said condition is situated in said operating program. In an embodiment of the invention, said operating program may include different, successively increasing pairs of threshold values of time and water volume, possibly corresponding to different performance requirements. For instance, the lowest pair may correspond to the requirement that the purified water be absolutely sterile and the higher pairs may correspond to the requirement that the purified water, while not being absolutely sterile, be potable or safely usable for other purposes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is an exploded, schematic cross-sectional view of an apparatus according to an embodiment of the invention, not showing a supporting housing; 
     FIGS. 2 and 3 illustrate at an enlarged scale, in axial cross-section and in horizontal cross-section on plane III—III of FIG. 2, looking in the direction of the arrows, an embodiment of filter unit employed in the apparatus of FIG. 1; 
     FIGS. 4 and 5 illustrate, in axial cross-section and in two different operating phases, an embodiment of a dosing unit and FIG. 4 a  is a horizontal cross-section of a detail of FIG. 4; 
     FIGS. 6 to  8  show in schematic cross-sections, on the planes indicated by corresponding roman letters in FIG. 9, an apparatus according to an embodiment of the invention; 
     FIG. 9 illustrates the disposition of the components of the same apparatus in horizontal cross-section; 
     FIG. 10 is a block diagram illustrating the electronic system of the apparatus; 
     FIG. 11 graphically illustrates an operating diagram of the system of FIG. 10; 
     FIGS. 12 and 13 schematically illustrates, in plan view and vertical cross-section, an embodiment of a main filter component; 
     FIG. 14 is a cross-section of an element of said component at an enlarged scale; 
     FIG. 15 is a cross-section of an embodiment of the inlet bottle holder; and 
     FIG. 16 is a schematic, exploded, perspective view of an embodiment of a filter unit. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 is an exploded schematic representation of an embodiment of the invention. The components of the machine are not shown in their actual positioned relationship, and the supporting housing is not shown. The power supply means, which are conventional, are also not shown. 
     In this embodiment, a gas cylinder  10  is mounted on a cylinder holder generally indicated at  11 . The cylinder holder may be of any kind adapted for liquid aerating machines and may be, in particular, such as described in the aforesaid EP 0 472 995 B1. Another cylinder holder, which is part of an embodiment of the invention, is schematically illustrated in FIGS. 4 and 5. In general, the gas cylinder holder will comprise means, such as screw means  12 , for attaching the gas cylinder  10  to it, and comprise a gas cylinder valve, unless this is part of the gas cylinder itself. The gas cylinder valve, which is not shown in detail in FIG. 1, is generally indicated at  13 , and this, as does for instance the cylinder holder of the aforesaid EP, comprises a valve outlet, a valve poppet which is urged by elastic means to close said valve outlet, and a plunger, indicated in FIG. 1 at  14 , which can be depressed by means of a lever  15  to force the poppet, against the reaction of the elastic means, to open the outlet and allow gas to escape from the gas cylinder. In the mechanism schematically represented in FIG. 1, gas will continue to escape from the gas cylinder as long as lever  15  is depressed by the operator. Alternatively, a dosing unit can be provided to cause a predetermined amount of gas to escape from the gas cylinder each time said dosage unit is actuated. 
     An embodiment of a dosage unit is shown in FIGS. 4 and 5 in schematic cross-section on a plane passing through the axis of the gas cylinder outlet valve. Said dosage unit comprises a gas reservoir  62  which is connected by passage  63  to the cylindrical space in which plunger  14  is housed. The said space communicates with conduit  16 ′, which is the inlet of conduit  16 . In this embodiment of the device, the plunger  14  is provided, at its lowermost end, with a head  64  which is so shaped as to seal the outlet of the chamber housing the gas outlet valve, generally indicated at  65 . The gas cylinder valve poppet is not shown, except for its tip  66 , which is in contact with head  64  of plunger  14 . Plunger  14  is furthermore provided with two peripheral seal rings  67  and  67 ′. The cylinder in which plunger  14  is housed is provided with cut-offs  68  and  68 ′ on two planes, as shown in the detail of FIG. 4 a , which is a cross-section of plunger  14  through the plane of cut-offs  68 , but is identical to a cross-section  14  through the plane of cut-offs  68 ′. 
     In the position of FIG. 4, lever  15  has been depressed to release gas. Plunger  14  has pressed down on gas cylinder valve poppet, thus opening the cylinder valve, seal ring  67 ′ does not prevent the passage of gas because of the presence of cut-offs  68 ′, and gas escapes from the cylinder and fills gas reservoir  62  through passage  63 . When lever  15  is released, the device assumes the position of FIG.  5 . Seal ring  67 ′ has risen above cut-offs  68 ′ and therefore prevents any gas passage from the gas cylinder to the reservoir  62 . However, concurrently, seal ring  68  has risen to the level of cut-offs  67 , so that gas can escape from reservoir  62  through conduit  63  and through said cutt-offs to conduit  16 ′ and thence to conduit  16 . In this way, the amount of gas which has filled reservoir  62  is fed to the water bottle each time that the plunger  14  or lever  15  is depressed and released. 
     The gas escapes through conduit  16  and at the inlet of said conduit passes through a pre-filter  17  which is a small block of porous material fixed to the outlet of the cylinder holder and which retains unwanted particles that may block the subsequent gas passageways. This filter will also perform as a safety feature, as it will reduce the risk of liquid carbon dioxide entering the main filter unit, hereinafter described. 
     An embodiment of inlet bottle holder is illustrated at an enlarged scale in FIG.  15 . An unfiltered water bottle  20  is held in said holder, generally indicated at  21 . The inlet bottle holder has an inlet  22  for gas conduit  16  and may be fixed or pivoted to the supporting structure (not shown in FIG. 1) and have a thread or bayonet  105  to secure the bottle  20  in position. If a thread is used, it should be different from that used for attaching the filtered water bottle to the dispense bottle holder, hereinafter described. The inlet water holder  21  also has a water outlet  23  leading to unfiltered water conduit  32 . Water outlet  23  is connected, at its lower end, to the upper, outlet end of a dip tube  24 . Dip tube  24  is preferably provided at its inlet end with a filter  31  to prevent larger particles, that may be present in the unfiltered water, from entering the filter unit. Preferably, dip tube  24  is separate from the bottle  20  and fits into it, thereby making its insertion easier. In a preferred form of the invention, the holder  21  also houses an exhaust valve  26  and a safety valve  27 , which both open when a bottle of unfiltered water is loaded onto the holder. These valves, only schematically illustrated in FIG. 15, may be of any type, e.g. such as described in cited EP 0 472 995 B1. If the holder  21  is pivoted, the valves will open when it is swung outwards to permit loading an unfiltered water bottle  20 . 
     The holder  21  can also house a counter  28 , of any convenient type, for counting the number of bottle insertions, and therefore, since each bottle has a given volume, the amount of water which is filtered. The counter may be resettable manually or automatically when the filter unit is replaced. The holder  21  may also house a pressure sensor  29 , which is a pressure switch set to pass an electrical signal when the pressure rises above a predetermined pressure, for instance, 0.5 bar. As the system pressure is very unlikely to drop below said pressure, e.g. 0.5 bar, during the operation of the machine, it can be assumed that each time the said signal has been given, the machine has been used once and an amount of water corresponding to the volume of the said bottle, say 1 liter, has been filtered. Each time that an empty bottle is removed, any remaining pressure is discharged, and each time a new, full one is mounted on the bottle holder, the pressure must be re-established, so that counting the times that said predetermined pressure is exceeded means counting the number of times that a bottle has been emptied and therefore the number of liters of water passing through the machine. Non-return valve  30  may also be incorporated in the gas inlet of holder  21 , to ensure that no water siphons back from bottle  20  to cylinder holder  11 . 
     When gas under pressure is introduced into bottle  20 , unfiltered water flows out through water outlet  23  and from it through a conduit  32 , to reach a filter base generally indicated at  35 . Filter base  35  has an inlet  36 , an inlet chamber  37 , an outlet chamber  38  and an outlet  40 . Inlet chamber  37  and outlet chamber  38  are separated by a UV source or lamp  42 . Filter base  35  is also provided with a peripheral retaining wall  43 , having an external ring  44  which comprises an upper flange  45 . The filter base  35  is also provided with electronic connections to the filter unit to be described, which are not shown, as well as with power supply means, also not shown. 
     The filter unit, which fits into the filter base, and is schematically illustrated in exploded perspective view in FIG.  16  and in axial cross-section in FIG. 2, is generally indicated at  50 . The filter unit is held in connection with the base  35  by a bayonet sleeve  51 , which clamps the filter to the base by using the flange around the opening of the filter, as seen in the cross-section of FIG.  3 . Both the flange  45  and the bayonet sleeve  51  extend along two opposed arcs of 90° each and are interrupted elsewhere. When the said arcs of flange  45  and sleeve  51  are in the same angular position, they clamp the filter to the base. When said arcs are relatively displaced by 90°, the filter is disengaged and can be lifted from the base. The filter unit  50  is provided with a housing generally indicated at  52 , in which is fixed or molded a central tube  53 , the bottom inlet of which fits into a sleeve  58  of the filter base. Water flows from inlet chamber  37  of the filter base around the UV lamp  42 , into tube  53 , through a pre-filter  54 , which contains a silver impregnated slug  55 , into an upper chamber  57  of the filter unit. A float blow valve  56  is provided for releasing trapped air. 
     The main filter component, in the embodiment being described, is constituted by a number of filter elements  60  mounted on a plate  61 , as shown in FIGS. 12 and 13. Each filter element comprises a pre-filter or depth filter and a microporous membrane, and is preferably of the type described in a copending Israeli Patent Application, Attorney&#39;s docket No. 4364, the contents of which are incorporated herein entirely by reference. 
     An embodiment of such a filter element  60  is shown in FIG.  14 . It comprises two outer layers of depth filter or prefilter  91  and  91 ′, which are preferably made of glass fiber. Internally of layers  91  and  91 ′, the filter element comprises layers  92  and  92 ′ pf microporous membrane, preferably having a practically complete (more than 99%) retentivity for microorganisms, which are supported respectively on support fabrics  93  and  93 ′. All the aforesaid layers are arranged symmetrically about a substantially open plastic netting  94 , which constitutes a drainage layer to conduct away the fluid passing through the aforesaid layers  91 - 91 ′,  92 - 92 ′, and  93 - 93 ′. Depth filter layers  91 - 91 ′ and microporous membrane layers  92 - 92 ′ are congruent at the top and sealed together at  95  by means of adhesive or by welding. They are also sealed together at the edges  102 . The drainage layer  94  and the fabric support layers  93 - 93 ′ do not extend up to the top of the element, viz. to the seal  95 , although, in an embodiment of the invention in which welding is used, the layers  93  and  93 ′ may reach to the edge seal and be sealed thermoplastically together. In FIGS. 12 and 13, described hereinafter, prefilter layers  91 - 91 ′ do not reach to the bottom of the element, but the microporous membrane layers, support fabric layers and drainage layers protrude beyond them towards the bottom. The depth filter layers  91 - 91 ′ are sealed at the bottom at  100 - 100 ′ and laterally at  102  to the microporous membrane layers  92 - 92 ′. Support layers  93 - 93 ′ and drainage layer  94  are narrower than the other layers and do not take part in seals  102 . 
     Filtering means, in this embodiment a number of filter elements  60 , are mounted on plate  61 , as particularly illustrated in FIGS. 12 and 13. Plate  61 , preferably but not necessarily circular, has a number of slits  101 , one for each element  60 . A filter elements  60  is passed through each of said slits, in such a way that their edges  100  are at the same level as the upper edge of plate  61 . The filter elements are then potted to plate  61  by filling the empty space between them and the inner edges the slits of plate  61  with a suitable adhesive  103 , so that no path of fluid flow exists between the elements  60  and the plate  61 . 
     The water passes from chamber  57  through the various layers of each element  60 , entering from outer depth layers  91 - 91 ′ and exiting from drainage layer  94 , and reaches chamber  59 , defined by plate  61  and by a carbon filter  70 . Then, the water passes into a second chamber  71 ′ defined by said carbon filter  70  and by retaining plate  72 , directing the filtered water into a liter-counter  73  and around a shut-off device  74  of the sealing plate  71 . This assures that when the predetermined, recommended volume water has flowed through the filter unit, the shut-off becomes active and the filter is rendered non-usable. The shut-off feature can also be actuated by an electronic central control unit to render the filter non-usable after a period of time or a predetermined volume of water has passed through the filter, or it can be actuated by mechanical means. This time and liter-counter may be stored electronically in a small printed circuit board  75  fixed to the filter and which is placed in electrical contact when the filter is fitted into the base. 
     From the liter-counter  73 , the water flows into the outlet chamber  38  of the filter base, around the UV lamp and in the passages  40 , and therefrom into a flow control device  76  of any suitable type. From the flow control device  76 , the filtered water flows at constant and controlled flow rate through a conduit  77  into a dispense bottle holder  78 , which has an inlet  79  at the end of which is preferably located a silver impregnated porous block  80 . Dispense bottle holder  78  is open to the atmosphere to prevent the build-up of any back pressure. The filtered, purified water gathers into a dispense bottle  81 , e.g., having a volume e.g. of one liter and at any rate the same volume as the unfiltered water bottle. To assist the insertion of the dispense bottle holder, this may be pivoted on the housing and support as such in the same way as the unfiltered water holder is pivoted. 
     The filter unit preferably contains a non-volatile memory to store the number of liters filtered, an identity number and a timer powered by an on-board battery, to measure elapsed time from the start up of the filter. The pressure sensor sends a signal to the CPU each time the pressure of the system raises above a pre-set figure. The display is mounted on the front of the machine and displays the condition of the filter by a series of LED&#39;s. A reset button is provided to be used by the operator after replacing a cylinder. The filter reset is automatic when a new filter is fitted and the electronic connections are made. 
     The structure and operation of a particular embodiment of the electronic control unit will now be described FIG. 10 is a block diagram of such a unit, generally indicated at  99 . The control unit counts the time and the water volume, which is conveniently expressed as a number of bottles of unfiltered water which have passed through the machine. The time memory (indicated in the diagram as “gas display”) controls a first display which has three display lights, for instance, red, amber and green and correspondingly indicated in the drawing by R, A and G, as well as a reset button. The volume memory (indicated in the diagram as “filter life”) controls another display which has three display lights having the same colors and additionally a fourth light which may be, for example, red, as well. A pressure sensor is also connected to the CPU, as is a solenoid which operates as hereinafter set forth. 
     The memory of the CPU contains an operating program which is graphically and schematically illustrated in FIG. 11, wherein the abscissa is the time, e.g., in hours, and the ordinate the volume count e.g., in liters. In the diagram, are defined three maxima for the volume count and three maxima for the time, which maxima limit three areas, respectively green, amber and red. These may correspond to three different operating requirements. The lowest maxima may provide sterile water, the intermediate ones potable water, and the highest ones water that is safe for other purposes. The CPU is programmed to compare the identity of the filter to the machine number. If the identity of the filter matches the machine number, the filter is new, is accepted and the machine operates as hereinafter set forth. If it does not match, a red signal is displayed and the machine is disabled, as hereinafter set forth. 
     When the operation of the apparatus is started, the pressure sensor is activated and the timer is activated. The pressure sensor sends the signals through the CPU to the volume count of the control unit. The timer in the control unit counts the time. At predetermined time intervals, for example, each hour, the CPU compares the volume count and the time to the memorized program of FIG.  11 . If neither the lowest maximum volume nor the lowest maximum time have been exceeded, the green light is activated: the apparatus continues to operate. If either the of said volume count or time is exceeded, the corresponding amber light is activated. If either the intermediate maximum volume count or the intermediate maximum time are exceeded, the corresponding red light is activated. The action to be taken in each case, e.g., the replacement of the filter, depends on the user&#39;s requirements. If the highest maximum volume count or the highest maximum time are exceeded, the second red light is also activated, indicating a situation of danger and the machine is disabled by energizing a solenoid, which moves a pin into such a position so to prevent the lever, that causes the feeding of gas to the unfiltered water bottle ( 15  in FIGS. 4 and 5) from being depressed, whereby the machine is rendered unusable. The solenoid is preferably of the latching type, and requires only short pulse signals to change its state. The CPU, however, could be programmed, according to the user&#39;s requirements, to actuate the solenoid before then, e.g. when one or both of the intermediate or even the lowest maxima has been reached, When the filter has been changed, all the memories are reset to 1. 
     While an embodiment of the invention has been described by way of illustration, it will be apparent that the invention may be carried out by persons skilled in the art with many modifications, variations and adaptations, without departing from its spirit or exceeding the scope of the claims