Chapter 9—Plumbing

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-1

Elements of a Plumbing System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-1

Water Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-1

Hot and Cold Water Main Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-3

Water Heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-7

Drainage System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-8

Corrosion Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-13

Water Conservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-13

Putting It All Together . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-14

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-15

Additional Sources of Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-16

Figure 9.1. Typical Home Water System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-1

Figure 9.2. House Service Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-2

Figure 9.3. Gas Water Heater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-7

Figure 9.4. Temperature-pressure Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-8

Figure 9.5. Branch Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-10

Figure 9.6. P-trap. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-10

Figure 9.7. Types of S-traps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-10

Figure 9.8. Trap Seal: (a) Seal Intact; (b) Fixture Draining; (c) Loss of Gas Seal . . . . . . . . . . . .9-10

Figure 9.9. Loss of Trap Seal in Lavatory Sink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-11

Figure 9.10. Back-to-back Venting (Toilet). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-11

Figure 9.11. Back-to-back Venting (Sink). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-11

Figure 9.12. Wall-hung Fixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-12

Figure 9.13. Unit Vent Used in Bathtub Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-12

Figure 9.14. Toilet Venting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-12

Figure 9.15. Janitor’s Sink. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-13

Figure 9.16. Common Y-trap. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-13

Figure 9.17. Hose Bib With Vacuum Breaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-13

Table 9.1. Fixture Unit Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-9

Table 9.2. Sanitary House Drain Sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-9

Table 9.3. Minimum Fixture Service Pipe Diameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-12

Healthy Housing Reference Manual 1

Contents
“The society which scorns excellence in plumbing as a

humble activity and tolerates shoddiness in philosophy

because it is an exalted activity will have neither good

plumbing nor good philosophy: neither its pipes nor its

theories will hold water.” 

John W. Gardner, Secretary, 

Department of Health, Education, and Welfare, 1965 

Introduction

Plumbing may be defined as the practice, materials, and

fixtures used in installing, maintaining, and altering

piping, fixtures, appliances, and appurtenances in

connection with sanitary or storm drainage facilities, a

venting system, and public or private water supply

systems. Plumbing does not include drilling water wells;

installing water soften ing equipment; or manufacturing

or selling plumbing fixtures, appliances, equipment, or

hardware. A plumbing system consists of three parts: an

adequate potable water supply system; a safe, adequate

drainage system; and ample fixtures and equipment.

The housing inspector’s prime concern while inspecting

plumbing is to ensure the provision of a safe water

supply system, an adequate drainage system, and ample

and proper fixtures and equipment that do not

contaminate water. The inspector must make sure that

the system moves waste safely from the home and

protects the occupants from backup of waste and

dangerous gases. This chapter covers the major features

of a residential plumbing system and the basic plumbing

terms and principles the inspector must know and

understand to identify housing code violations that

involve plumbing. It will also assist in identifying the

more complicated defects that the inspector should refer

to the appropriate agencies. This chapter is not a

plumbing code, but should provide a base of knowledge

sufficient to evaluate household systems. 

Elements of a Plumbing System 

The primary purposes of a plumbing system are

• To bring an adequate and potable supply of hot

and cold water to the inhabitants of a house, and

• To drain all wastewater and sewage discharge

from fixtures into the public sewer or a private

disposal system.

It is, therefore, very important that the housing inspector

be completely familiar with all elements of these systems

so that inade quacies of the structure’s plumbing and

other code violations will be recognized. To aid the

inspector in understanding the plumbing system, a schematic

of a home plumbing system is shown in Figure 9.1.

Water Service

The piping of a house service line should be as short as

possible. Elbows and bends should be kept to a minimum

because they reduce water pressure and, therefore, the

supply of water to fixtures in the house. The house

service line also should be protected from freezing.

Four feet of soil is a commonly accepted depth to bury

the line to prevent freezing. This depth varies, however,

across the country from north to south. The local or state

plumbing code should be consulted for recommended

depths. The minimum service line size should be 3⁄4 inch.

The minimum water supply pressure should be 40 pounds

per square inch (psi), no cement or concrete joints

should be allowed, no glue joints between different types

of plastic should be allowed, and no female threaded

PVC fittings should be used.

The materials used for a house service may be approved

plastic, copper, cast iron, steel, or wrought iron. The

connections used should be compatible with the type of

pipe used. A typical house service installation is pictured

in Figure 9.2. The elements of the service installation are

described below. 

Corporation stop—The corporation stop is connected to

the water main. This connection is usually made of brass

Chapter 9: Plumbing

Healthy Housing Reference Manual 9-1

Figure 9.1. Typical Home Water System [1]
and can be connected to the main with a special tool

without shutting off the municipal supply. The valve

incorporated in the corporation stop permits the pressure

to be maintained in the main while the service to the

building is completed. 

Curb stop—The curb stop is a similar valve used to

isolate the building from the main for repairs,

nonpayment, of water bills or flooded basements. Because

the corporation stop is usually under the street and it is

necessary to break the pavement to reach the valve, the

curb stop is used as the isolation valve.

Curb stop box—The curb stop box is an access box to

the curb stop for opening and closing the valve. A longhandled wrench is used to reach the valve.

9-2 Plumbing

Air chambers—Pressure-absorbing devices that eliminate water hammer. Air chambers should be installed as close as possible

to the valves or faucet and at the end of long runs of pipe.

Air gap (drainage system)—The unobstructed vertical distance through the free atmosphere between the outlet of a water

pipe and the flood level rim of the receptacle into which it is discharging.

Air gap (water distribution system)—The unobstructed vertical distance through the free atmosphere between the lowest

opening from any pipe or faucet supplying water to a tank, plumbing fixture, or other device and the flood level rim of the

receptacle.

Backflow—The flow of water or other liquids, mixtures, or substances into the distributing pipes of a potable water supply from any source or sources other than the intended source. Back siphonage is one type of backflow. 

Back siphonage—The flowing back of used, contaminated, or polluted water from a plumbing fixture or vessel into a

potable water supply because of negative pressure in the pipe. 

Branch—Any part of the piping system other than the main, riser, or stack.

Branch vent—A vent connecting one or more individual vents with a vent stack.

Building drain—Part of the lowest piping of a drainage system that receives the discharge from soil, waste, or other

drainage pipes inside the walls of the building (house) and conveys it to the building sewer beginning 3 feet outside the

building wall.

Cross connection—Any physical connection or arrangement between two otherwise separate piping systems (one of

which contains potable water and the other which contains either water of unknown or questionable safety or steam, gas,

or chemical) whereby there may be a flow from one system to the other, the direction of flow depending on the pressure differential between the two systems. (See Backflow and Back siphonage.)

Disposal field—An area containing a series of one or more trenches lined with coarse aggregate and conveying the effluent from a septic tank through vitrified clay pipe or perforated, nonmetallic pipe, laid in such a manner that the flow will

be distributed with reasonable uniformity into natural soil.

Drain—Any pipe that carries wastewater or waterborne waste in a building (house) drainage system.

Flood level rim—The top edge of a receptacle from which water overflows. 

Flushometer valve—A device that discharges a predetermined quantity of water to fixtures for flushing purposes and is

closed by direct water pressures. 

Flushometer toilet—a toilet using a flushometer valve that uses pressure from the water supply system rather than the

force of gravity to discharge water into the bowl, designed to use less water than conventional flush toilets.

Flush valve—A device located at the bottom of the tank for flushing toilets and similar fixtures.

Definitions of Terms Related to Home Water Systems

Figure 9.2. House Service Installation [1]
Meter stop—The meter stop is a valve placed on the

street side of the water meter to isolate it for installation

or maintenance. Many codes require a gate valve on the

house side of the meter to shut off water for plumbing

repairs. The curb and meter stops can be ruined in a short

time if used very frequently. 

The water meter is a device used to measure the amount

of water used in the house. It is usually the property of

the water provider and is a very delicate instrument that

should not be abused. In cold climates, the water meter is

often inside the home to keep it from freezing. When the

meter is located inside the home, the company providing

the water must make appointments to read the meter,

which often results in higher water costs unless the meter

is equipped with a signal that can be observed from the

outside. The water meter is not shown in Figure 9.2

because of regional differences in location of the unit. 

Because the electric system is sometimes grounded to an

older home’s water line, a grounding loop device should

be installed around the meter. Many meters come with a

yoke that maintains electrical continuity even though the

meter is removed.

Hot and Cold Water Main Lines

The hot and cold water main lines are usually hung from

the basement ceiling or in the crawl space of the home

and are attached to the water meter and hot water tank

on one side and the fixture supply risers on the other. These

pipes should be installed neatly and should be supported by

pipe hangers or straps of sufficient strength and number to

Healthy Housing Reference Manual 9-3

z

Grease trap—See Interceptor.

Hot water—Potable water heated to at least 120°F–130°F (49°C–54°C) and used for cooking, cleaning, washing dishes,

and bathing.

Insanitary—Unclean enough to endanger health.

Interceptor—A device to separate and retain deleterious, hazardous, or undesirable matter from normal waste and permit

normal sewage or liquid waste to discharge into the drainage system by gravity.

Main vent—The principal artery of the venting system, to which vent branches may be connected.

Leader—An exterior drainage pipe for conveying storm water from roof or gutter drains to the building storm drain,

combined building sewer, or other means of disposal.

Main sewer—See Public sewer.

Pneumatic—Pertaining to devices making use of compressed air as in pressure tanks boosted by pumps.

Potable water—Water having no impurities present in amounts sufficient to cause disease or harmful physiologic effects

and conforming in its bacteriologic and chemical quality to the requirements of the U.S. Environmental Protection

Agency’s Safe Drinking Water Act or meeting the regulations of other agencies having jurisdiction.

P & T (pressure and temperature) relief valve—A safety valve installed on a hot water storage tank to limit temperature

and pressure of the water.

P-trap—A trap with a vertical inlet and a horizontal outlet.

Public sewer—A common sewer directly controlled by public authority.

Relief vent—An auxiliary vent that permits additional circulation of air in or between drainage and systems.

Septic tank—A watertight receptacle that receives the discharge of a building’s sanitary drain system or part thereof and

is designed and constructed to separate solid from liquid, digest organic matter through a period of detention, and allow

the liquids to discharge into the soil outside of the tank through a system of open-joint or perforated piping or through a

seepage pit.

Sewerage system—A system comprising all piping, appurtenances, and treatment facilities used for the collection and 

disposal of sewage, except plumbing inside and in connection with buildings served, and the building drain.

Soil pipe—The pipe that directs the sewage of a house to the receiving sewer, building drain or building sewer.

Soil stack—The vertical piping that terminates in a roof vent and carries off the vapors of a plumbing system.

Stack vent—An extension of a solid or waste stack above the highest horizontal drain connected to the stack, sometimes

called a waste vent or a soil vent.

Definitions of Terms Related to Home Water Systems
prevent sagging. Older homes that have copper pipe with

soldered pipes can pose a lead poisoning risk, particularly

to children. In 1986, Congress banned lead solder

containing greater than 0.2% lead and restricted the lead

content of faucets, pipes, and other plumbing materials to

no more than 8%. The water should be tested to

determine the presence or level of lead in the water. Until

such tests can be conducted, the water should be run for

about 2 minutes in the morning to flush any such

material from the line. Hot and cold water lines should

be approximately 6 inches apart unless the hot water line

is insulated. This is to ensure that the cold water line does

not pick up heat from the hot water line [2].

The supply mains should have a drain valve stop and waste

valve to remove water from the system for repairs. These

valves should be on the low end of the line or on the end of

each fixture riser.

The fixture risers start at the basement main and rise

vertically to the fixtures on the upper floors. In a onefamily dwelling, riser branches will usually proceed from

the main riser to each fixture grouping. In any event, the

fixture risers should not depend on the branch risers for

support, but should be supported with a pipe bracket.

The size of basement mains and risers depends on the

number of fixtures supplied. However, a 3⁄4-inch pipe is

usually the minimum size used. This allows for deposits

on the pipe due to hardness in the water and will usually

give satisfactory volume and pressure.

In homes without basements, the water lines are

preferably located in the crawl space or under the slab.

The water lines are sometimes placed in the attic;

however, because of freezing, condensation, or leaks, this

placement can result in major water damage to the home.

In two-story or multistory homes, the water line

placement for the second floor is typically between the

studs and, then, for the shortest distance to the fixture,

between the joists of the upper floors.

Hot and Cold Water Piping Materials

Care must be taken when choosing the piping materials.

Some state and local plumbing codes prohibit using some

of the materials listed below in water distribution systems.

Polyvinyl Chloride (PVC). PVC is a white plastic pipe

used outside. It should be used only for cold water. Its

uses include water service between the meter and building

and irrigation [3]. PVC, or vinyl, is one of the most

commonly used materials in the marketplace. It is in

water pipes, packaging, construction and automotive

material, toys, and medical equipment. PVC is also

known as chloroethene, chloroethylene, and ethylene

monochloride. It is a known human carcinogen; PVC

causes liver cancer, angiosarcomas, and other health

problems in people who are exposed to it in their work

environment. Significant exposure can occur when the

material is heated or in the process of manufacturing the

material. As a result, PVC is closely regulated in the work

environment and not commonly recommended for use as

hot water piping. 

9-4 Plumbing

Storm sewer—A sewer used for conveying rain water, surface water, condensate, cooling water, or similar liquid waste.

Trap—A fitting or device that provides a liquid seal to prevent the emission of sewer gases without materially affecting

the flow of sewage or wastewater through it.

Vacuum breaker—A device to prevent backflow (back siphonage) by means of an opening through which air may be drawn

to relieve negative pressure (vacuum).

Vapor lock—A bubble of air that restricts the flow of water in a pipe.

Vent stack—The vertical vent pipe installed to provide air circulation to and from the drainage system and that extends

through one or more stories.

Water hammer—The loud thump of water in a pipe when a valve or faucet is suddenly closed.

Water service pipe—The pipe from the water main or other sources of potable water supply to the water-distributing 

system of the building served.

Water supply system—Consists of the water service pipe, the water-distributing pipes, the necessary connecting pipes, 

fittings, control valves, and all appurtenances in or adjacent to the building or premises.

Wet vent—A vent that receives the discharge of waste other than from water closets.

Yoke vent—A pipe connecting upward from a soil or waste stack to a vent stack to prevent pressure changes in the stacks.

Definitions of Terms Related to Home Water Systems
PVC also contains phthalates, which accumulate in body

tissues and can damage the liver and lungs. It has been

shown in lower mammals to damage reproductive organs.

Phthalates are freely given off by the plastics in which it is

used; and, because it is fat soluble, is found in meats and

cheeses packaged in PVC. Although phthalates show

almost no toxicity in adult humans in acute (short-term)

doses, even at high doses, the cumulative nature of

phthalate toxicity results in toxic effects even at very low

dosages with chronic exposure (over a long period of

time). Very young infants do not metabolize phthalates as

well as do adults, and so are at greater risk for harm. The

availability of phthalates in the consumer environment

causes inevitable chronic ingestion for almost all modern

industrial consumers. 

Lead is used as a hardening agent to manufacture PVC

materials. Therefore, it is very important that third-party

testing be done on PVC piping. PVC piping should have

the stamp of both the testing laboratory and a potable

water (PW) mark to indicate that it meets appropriate

standards for use as potable water piping. 

Chlorinated PVC (CPVC). CPVC is a slightly yellow

plastic pipe used inside homes. It has a long service life,

but is not quite as tough as copper. Some areas with

corrosive water will benefit by using chlorinated PVC

piping. CPVC piping is designed and recommended for

use in hot and cold potable water distribution systems [4].

Copper. Copper comes in three grades: 

• M for thin wall pipe (used mainly inside homes); 

• L for thicker wall pipe (used mainly outside for

water services); and 

• K, the thickest (used mainly between water mains

and the water meter). 

Copper lasts a long time, is durable, and connects well to

valves. It should not be installed if the water has a pH of

6.5 or less. Most public utilities supply water at a pH

between 7.2 and 8.0. Many utilities that have source

water with a pH below 6.5 treat the water to raise the

pH. Private well water systems often have a pH below

6.5. When this is the case, installing a treatment system

to make the water less acidic is a good idea [5].

Galvanized Steel. Galvanized pipe corrodes rather easily.

The typical life of this piping is about 40 years. One of

the primary problems with galvanized steel is that, in

saturated water, the pipe will become severely restricted

by corrosion that eventually fills the pipe completely.

Another problem is that the mismatch of metals between

the brass valves and the steel results in corrosion.

Whenever steel pipe meets copper or brass, the steel pipe

will rapidly corrode. Dielectric unions can be used

between copper and steel pipes; however, these unions

will close off flow in a short time. The problem with

dielectric unions is that they break the grounding effect if

a live electrical wire comes in contact with a pipe. Some

cities require the two pipes to be bonded electrically to

maintain the safety of grounded pipes. 

PEX. PEX is an acronym for a cross-formulated

polyethylene. “PE” refers to the raw material used to make

PEX (polyethylene), and “X” refers to the cross-linking of

the polyethylene across its molecular chains. The

molecular chains are linked into a three-dimensional

network that makes PEX remarkably durable within a wide

range of temperatures, pressures, and chemicals [6].

PEX is flexible and can be installed with fewer fittings

than rigid plumbing systems. It is a good choice for

repiping and for new homes and works well for corrosive

water conditions. PEX stretches to accommodate the

expansion of freezing water and then returns to its

original size when water thaws. Although it is highly

freeze-resistant, no material is freeze-proof. 

Kitec. Kitec is a multipurpose pressure pipe that uniquely

unites the advantages of both metal and plastic. It is made

of an aluminum tube laminated to interior and exterior

layers of plastic. Kitec provides a composite piping system

for a wide range of applications, often beyond the scope of

metal or plastic alone. Unlike copper and steel materials,

Kitec is noncorroding and resists most acids, salt

solutions, alkalis, fats, and oils. 

Poly. Poly pipe is a soft plastic pipe that comes in coils

and is used for cold water. It can crack with age or wear

through from rocks. Other weak points can be the

stainless steel clamps or galvanized couplings.

Polybutylene [Discontinued]. Polybutylene pipe is a soft

plastic pipe. This material is no longer recommended

because of early chemical breakdown. Individuals with a

house, mobile home, or other structure that has

polybutylene piping with acetal plastic fittings may be

eligible for financial relief if they have replaced that

plumbing system. For claims information, call 1-800-

392-7591 or go to www.pbpipe.com.

Healthy Housing Reference Manual 9-5
Hot Water Safety

In the United States, more than 112,000 people enter a

hospital emergency room each year with scald burns. Of

these, 6,700 (6%), have to be hospitalized. Almost 3,000 of

these scald burns come from tap water in the home. The

three high risk groups are children under the age of 5 years,

the handicapped, and adults over the age of 65 years. It

only takes 1 second to get a serious third-degree burn

from water that is 156°F (69°C). Tap water is too hot if

instant coffee granules melt in it.

Young children, some handicapped individuals, and

elderly people are particularly vulnerable to tap water

burns. Children cannot always tell the hot water faucets

from the cold water faucets. Children have delicate skin

and often cannot get out of hot water quickly, so they

suffer hot water burns most frequently. Elderly and

handicapped persons are less agile and more prone to falls

in the bath tub. They also may have diseases, such as

diabetes, that make them unable to feel heat in some

regions of the body, such as the hands and feet. Thirddegree burns can occur quickly—in 1 second at 156°F

(69°C), in 2 seconds at 149°F (65°C), in 5 seconds at

140°F (60°C), and in 15 seconds at 133°F (56°C).

A tap-water temperature of 120°F–130°F (49°C–54°C) is

hot enough for washing clothes, bedding, and dishes.

Even at 130°F (54°C), water takes only a few minutes of

constant contact to produce a third-degree burn. Few

people bathe at temperatures above 110°F (43°C), nor

should they. Water heater thermostats should be set at

about 120°F (49°C) for safety and to save 18% of the

energy used at 140°F (60°C). Antiscald devices for faucets

and showerheads to regulate water temperature can help

prevent burns. A plumber should install and calibrate

these devices. Most hot water tank installations now

require an expans ion tank to reduce pressure fluctuations

and a heat trap to keep hot water from escaping up pipes.

Types of Water Flow Controls

It is essential that valves be used in a water system to

allow the system to be controlled in a safe and efficient

manner. The number, type, and size of valves required

will depend on the size and complexity of the system. Most

valves can be purchased in sizes and types to match the

pipe sizes used in water system installations. Listed below

are some of the more commonly encountered valves with

a description of their basic functions.

Shutoff Valves. Shutoff valves should be installed between

the pump and the pressure tank and between the pressure

tank and service entry to a building. Globe, gate, and ball

valves are common shutoff valves. Gate and ball valves

cause less friction loss than do globe valves; ball valves last

longer and leak less than do gate valves. Shutoff valves

allow servicing of parts of the system without draining the

entire system.

Flow-control Valves. Flow-control valves provide uniform

flow at varying pressures. They are sometimes needed to

regulate or limit the use of water because of limited water

flow from low-yielding wells or an inadequate pumping

system. They also may be needed with some treatment

equipment. These valves are often used to limit flow to a

fixture. Orifices, mechanical valves, or diaphragm valves

are used to restrict the flow to any one service line or

complete system and to assure a minimum flow rate to all

outlets.

Relief Valves. Relief valves permit water or air to escape

from the system to relieve excess pressure. They are

spring-controlled and are usually adjustable to relieve

varying pressures, generally above 60 psi. Relief valves

should be installed in systems that may develop pressures

exceeding the rated limits of the pressure tank or

distribution system. Positive displacement and

submersible pumps and water heaters can develop these

excessive pressures. The relief valve should be installed

between the pump and the first shutoff valve and must be

capable of discharging the flow rate of the pump. A

combined pressure and temperature relief valve is needed

on all water heaters. Combination pressure and vacuum

relief valves also should be installed to prevent vacuum

damage to the system.

Pressure-reducing Valves. A pressure-reducing valve is

used to reduce line pressure. On main lines, this allows

the use of thinner walled pipe and protects house

plumbing. Sometimes these valves are installed on

individual services to protect plumbing.

Altitude Valves. Often an altitude valve is installed at the

base of a hot water tank to prevent it from overflowing.

Altitude valves sense the tank level through a pressure line

to the tank. An adjustable spring allows setting the level

so that the valve closes and prevents more inflow when

the tank becomes full.

Foot Valves. A foot valve is a special type of check valve

installed at the end of a suction pipe or below the jet in a

well to prevent backflow and loss of prime. The valve

should be of good quality and cause little friction loss.

9-6 Plumbing
Check Valves. Check valves have a function similar to

foot valves. They permit water flow in only one direction

through a pipe. A submersible pump may use several

check valves. One is located at the top of the pump to

prevent backflow from causing back spin of the impellers.

Some systems use another check valve and a snifter valve.

They will be in the drop pipe or pitless unit in the well

casing and allow a weep hole located between the two

valves to drain part of the pipe. When the pump is started,

it will force the air from the drained part of the pipe into

the pressure tank, thus recharging the pressure tank.

Frost-proof Faucets. Frost-proof faucets are installed

outside a house with the shutoff valve extending into the

heated house to prevent freezing. After each use, the water

between the valve and outlet drains, provided the hose is

disconnected, so water is not left to freeze.

Frost-proof Hydrants. Frost-proof hydrants make outdoor

water service possible during cold weather without the

danger of freezing. The shutoff valve is buried below the

frost line. To avoid submerging it, which might result in

contamination and back siphoning, the stop-and-waste

valve must drain freely into a rock bed. These hydrants

are sometimes prohibited by local or state health authorities.

Float Valves. Float valves respond to a high water level to

close an inlet pipe, as in a tank-type toilet.

Miscellaneous Switches. Float switches respond to a high

and/or low water level as with an intermediate storage

tank. Pressure switches with a low-pressure cutoff stop the

pump motor if the line pressure drops to the cutoff point.

Low-flow cutoff switches are used with submersible

pumps to stop the pump if the water discharge falls below

a predetermined minimum operating pressure. Highpressure cut-off switches are used to stop pumps if the

system pressure rises above a predetermined maximum.

Paddle-type flow switches detect flow by means of a

paddle placed in the pipe that operates a mechanical

switch when flow in the pipe pushes the paddle.

The inadvertent contamination of a public water supply

as a result of incorrectly installing plumbing fixtures is a

poten tial public health problem in all communities.

Continuous surveillance by environmental health

personnel is necessary to know whether such public

health hazards have developed as a result of additions or

alterations to an approved system. All environmental

health specialists should learn to recognize the three

general types of defects found in potable water supply

systems: backflow, back siphonage, and overhead leakage

into open potable water containers. If identified, these

conditions should be corrected immediately to prevent

the spread of disease or poisoning from high concentrations

of organic or inorganic chemicals in the water.

Water Heaters

Water heaters (Figure 9.3) are usually powered by

electricity, fuel oil, gas, or, in rare cases, coal or wood.

They consist of a space for heating the water and a

storage tank for providing hot water over a limited period

of time. All water heaters should be fitted with a

temperature-pressure (T&P) relief valve no matter what

fuel is used. The installation port for these valves may be

found on the top or on the side of the tank near the top.

T&P valves should not be placed close to a wall or door

jamb, where they would be inaccessible for inspection and

use. Hot water tanks sometimes are sold without the

T&P valve, and it must be purchased separately. This fact

alone should encourage individual permitting and

inspection by counties and municipalities to ensure that

they are installed. The T&P valve should be inspected at a

minimum of once per year.

A properly installed T&P valve will operate when either

the temperature or the pressure becomes too high due to

an interruption of the water supply or a faulty thermostat.

Figure 9.3 shows the correct installation of a gas water

Healthy Housing Reference Manual 9-7

Figure 9.3. Gas Water Heater [1]
heater. Particular care should be paid to the exhaust port

of the T&P valve. Figure 9.4 shows the placement of the

T&P valve. This vent should be directed to within

6 inches of the floor, and care must be taken to avoid

reducing the diameter of the vent and creating any

unnecessary bends in the discharge pipe. Most codes will

allow only one 90° bend in the vent. The point is to

avoid any constrictions that could slow down the steam

release from the tank to avoid explosive pressure buildup. 

Water heaters that are installed on wooden floors should

have water collection pans with a drainage tube that drains to

a proper drain. The pan should be checked on a regular basis.

Tankless Water Heaters 

A tankless unit has a heating device that is activated by

the flow of water when a hot water valve is opened. Once

activated, the heater delivers a constant supply of hot

water. The output of the heater, however, limits the rate

of the heated water flow. Demand water heaters are

available in propane (LP), natural gas, or electric models.

They come in a variety of sizes for different applications,

such as a whole-house water heater, a hot water source for

a remote bathroom or hot tub, or as a boiler to provide

hot water for a home heating system. They can also be

used as a booster for dishwashers, washing machines, and a

solar or wood-fired domestic hot water system [7]. 

The appeal of demand water heaters is not only the

elimination of the tank standby losses and the resulting

lower operating costs, but also the fact that the heater

delivers hot water continuously. Most tankless models

have a life expectancy of more than 20 years. In contrast,

storage tank water heaters last 10 to 15 years. Most

tankless models have easily replaceable parts that can

extend their life by many years more.

Drainage System

Water is brought into a house, used, and discharged

through the drainage system. This system is a sanitary

drainage system carrying just interior wastewater.

Sanitary Drainage System

The proper sizing of the sanitary drain or house drain

depends on the number of fixtures it serves. The usual

minimum size is 4 inches in diameter. The materials used

are usually cast iron, vitrified clay, plastic, and, in rare

cases, lead. The top two pipe choices for drain, waste, and

vent (DWV) systems are PVC or ABS. For proper flow in

the drain, the pipe should be sized and angled so that the

pipe is approximately half full. This ensures proper

scouring action so that the solids contained in the waste

will not be deposited in the pipe. 

Using PVC in DWV pipe is a two-step process needing a

primer and then cement. ABS uses cement only. In most

cases the decision will be made on the basis of which

material is sold in an area. Few areas stock both materials

because local contractors usually favor one or the other.

ABS costs more than PVC in many areas, but Schedule

40 PVC DWV solid core pipe is stronger than ABS.

Their durability is similar.

Size of House Drain. The Uniform Plumbing Code

Committee has developed a method of sizing house

drains in terms of fixture units. One fixture unit equals

approximately 71⁄2 gallons of water per minute. This is the

surge flow rate of water discharged from a wash basin in

one minute. 

All other fixtures have been related to this unit. Fixture

unit values are shown in Table 9.1.

Grade of House Drain. A house drain should be sloped

toward the sewer to ensure scouring of the drain. The

usual pitch of a house or building sewer is a 1⁄4-inch drop

in 1 foot of length. The size of the drain is based on the

fixture units flowing into the pipe and the slope of the

drain. Table 9.2 shows the required pipe size for the system.

9-8 Plumbing

Figure 9.4. Temperature-Pressure Valve
House Drain Installation. Typical branch connections to

the main are shown in Figure 9.5.

Fixture and Branch Drains. A branch drain is a waste

pipe that collects the waste from two or more fixtures and

conveys it to the sewer. It is sized in the same way as the

sewer, taking into account that all toilets must have a

minimum 3-inch diameter drain, and only two toilets

may connect into one 3-inch drain. All branch drains

must join the house drain with a Y-fitting as shown in

Figure 9.5. The same is true for fixture drains joining

branch drains. The Y-fitting is used to eliminate, as much

as possible, the deposit of solids in or near the

connection. A buildup of these solids will block the drain.

Recommended minimum sizes of fixture drains are shown

in Table 9.2. 

Traps 

A plumbing trap is a device used in a waste system to

prevent the passage of sewer gas into the structure and yet

not hinder the fixture’s discharge to any great extent. All

fixtures connected to a household plumbing system

should have a trap installed in the line. The effects of

sewer gases on the human body are well known; many of

the gases are extremely harmful. In addition, certain sewer

gases are explosive. 

P-trap. The most commonly used trap is the P-trap

(Figure 9.6). The depth of the seal in a trap is usually

2 inches. A deep seal trap has a 4-inch seal. 

As mentioned earlier, the purpose of a trap is to seal out

sewer gases from the structure. Because a plumbing

system is subject to wide variations in flow, and this flow

originates in many different sections of the system,

pressures vary widely in the waste lines. These pressure

differences tend to remove the water seal in the trap. The

waste system must be properly vented to prevent the traps

from siphoning dry, thus losing their water seal and

allowing gas from the sewer into the building. 

Objectionable Traps. The S-trap and the 3⁄4 S-trap

(Figure 9.7) should not be used in plumbing installations.

They are almost impossible to ventilate properly, and the

3⁄4 S-trap forms a perfect siphon. Mechanical traps were

introduced to counteract this problem. It has been found,

however, that the corrosive liquids flowing in the system

corrode or jam these mechanical traps. For this reason, most

plumbing codes prohibit mechanical traps.

Healthy Housing Reference Manual 9-9

Table 9.2. Sanitary House Drain Sizes 

Table 9.1. Fixture Unit Values 
The bag trap, an extreme form of S-trap, is seldom found. 

Figure 9.7 also shows this type of S-trap.

Traps are used only to prevent the escape of sewer gas into

the structure. They do not compensate for pressure

variations. Only proper venting will eliminate pressure

problems. 

Ventilation

A plumbing system is ventilated to prevent trap seal loss,

material deterioration, and flow retardation.

Trap Seal Loss. The seal in a plumbing trap may be lost

due to siphonage (direct and indirect or momentum),

back pressure, evaporation, capillary attraction, or wind 

effect. The first two are probably the most common

causes of loss. Figure 9.8 depicts this siphonage process;

Figure 9.9 depicts loss of trap seal. 

If a waste pipe is placed vertically after the fixture trap, as

in an S-trap, the wastewater continues to flow after the

fixture is emptied and clears

the trap. This is caused by the

pressure of air on the water of

the fixture being greater than

the pressure of air in the waste

pipe. The action of the water

discharging into the waste pipe

removes the air from that pipe

and thereby causes a negative

pressure in the waste line.

In the case of indirect or

momentum siphonage, the

flow of water past the entrance

to a fixture drain in the waste

pipe removes air from the

fixture drain. This reduces the

air pressure in the fixture

drain, and the entire assembly

acts as an aspirator. (Figures

9.10 and 9.11 show plumbing

configurations that would

allow this type of siphonage to

occur.) 

Back Pressure. The flow of

water in a soil pipe varies

according to the fixtures being

used. Small flows tend to cling

to the sides of the pipe, but

large ones form a slug of waste

as they drop. As this slug of

water falls down the pipe, the

air in front of it becomes

Figure 9.7. Types of S-traps

Figure 9.8. Trap Seal: [a]

Seal Intact; [b] Fixture

Draining; [c] Loss of Gas

Seal [1]

Figure 9.5. Branch Connections Figure 9.6. P-trap [1]

9-10 Plumbing
pressurized. As the pressure

builds, it seeks an escape

point. This point is either a

vent or a fixture outlet. If the

vent is plugged or there is no

vent, the only escape for this

air is the fixture outlet. 

The air pressure forces the

trap seal up the pipe into the

fixture. If the pressure is great

enough, the seal is blown out

of the fixture entirely. Figures

9.8 and 9.9 illustrate the

potential for this type of

problem. Large water flow past

the vent can aspirate the water

from the trap, while water

flow approaching the trap can

blow the water out of the trap.

Vent Sizing. Vent pipe installation is similar to that of soil

and waste pipe. The same fixture unit criteria are used.

Table 9.3 shows minimum vent pipe sizes.

Vent pipes of less than 11⁄4 inches in diameter should not

be used. Vents smaller than this diameter tend to clog and

do not perform their function.

Individual Fixture Ventilation. Figure 9.12 shows a

typical installation of a wall-hung plumbing unit. This

type of ventilation is generally used for sinks, drinking

fountains, and so forth. Air admittance valves are often

used for individual fixtures. Figure 9.13 shows a typical

installation of a bathtub or shower ventilation system.

Figure 9.14 shows the proper vent connection for toilet

fixtures and Figure 9.15 shows a janitor’s sink or slop sink

that has the proper P-trap. For the plumbing fixture to

work properly, it must be vented as in Figures 9.13 and 9.14.

Unit Venting. Figures 9.10 and 9.11 show a back-to-back

shared ventilation system for various plumbing fixtures.

The unit venting system is commonly used in apartment

buildings. This type of system saves a great deal of money

and space when fixtures are placed back-to-back in

separate apartments. It does, however, pose a problem if

the vents are undersized because they will aspirate the

water from the other trap. Figure 9.16 shows a double

combination Y-trap used for joining the fixtures to the

common soil pipe fixture on the other side of the wall.

Wet Venting. Bathroom fixture groupings are commonly

wet vented; that is, the vent pipe also is used as a waste line. 

Total Drainage System

The drain, soil waste, and vent systems are all connected, and

the inspector should remember the following fundamentals:

Working vents must provide air to all fixtures to ensure

the movement of waste into the sewer. Improperly vented

fixtures will drain slowly and clog often. They also present

a health risk if highly toxic and explosive sewer gases enter

the home. Correct venting is shown in Figures 9.10–9.15;

incorrect venting is shown in Figures 9.8 and 9.9. A wet

Healthy Housing Reference Manual 9-11

Figure 9.9. Loss of Trap Seal in

Lavatory Sink [1]

Figure 9.10. Back-to-back Venting [Toilet]

Figure 9.11. Back-to-back Venting [Sink]
vent can result in one of the traps siphoning the other dry

when large volumes of water are poured down the drain.

Wet vents are not permitted by many state plumbing

codes because of the potential for self-siphoning.

Backup of sewage into sinks, dishwashers, and other

appliances is always a possibility unless the system is

equipped with air gaps or vacuum breakers. All

connections to the potable water system must be a

minimum of two pipe diameters above the overflow of

the appliance and, in some cases, where flat surfaces are

near, two and one-half pipe diameters above the overflow

of the appliance.

A simple demonstration of how easily siphoning can

occur is to hold a glass of water with food coloring in it

with the tip of a faucet in the colored water. If the sink’s

vegetable sprayer is directed to a second glass and sprayed,

in most cases, the colored water will be aspirated into the

faucet and then out of the sprayer into the second glass.

Weed or pest killer attachments that hook to garden hoses

work on the same principle. Figure 9.17 shows an outside

hose bib equipped with a vacuum breaker. In the areas of

the United States that freeze, these vacuum breakers must

be removed because they trap water in the area of the line

that can freeze and burst. Many vacuum breakers sold

today automatically drain to prevent freeze damage. 

9-12 Plumbing

Figure 9.12. Wall-hung Fixtures 

Figure 9.13. Unit Vent Used in Bathtub Installation

Table 9.3. Minimum Fixture Service Pipe Diameters

Figure 9.14. Toilet Venting
Devices that pull water from a utility may create negative

pressures that can damage water piping and pull

dangerous substances into the line at the same time.

These devices include power sprayers that hook to the

home hose bib (outside faucets) and pressurize the spray

by creating a vacuum on the supply side.

Corrosion Control

To understand the proper maintenance procedures for the

prevention and elimination of water quality problems in

plumbing systems, it is necessary to understand the

process used to determine the chemical aggressiveness of

water. The process is used to determine when additional

treatment is needed. Water that is out of balance can

result in many negative outcomes, from toxic water to

damaged and ruined equipment. 

Water dissolves and carries materials when it is not

saturated. An equilibrium among pH, temperature,

alkalinity, and hardness controls water’s ability to create

scale or to dissolve material. If water is saturated with

harmless or beneficial substances, such as calcium, then

the threat of damage can be mitigated. The Langelier

method, developed in the early 1930s, is a process used in

boiler management,

municipal water

treatment, and

swimming pools to

provide this balance. In

the Langelier index,

saturation over 0.3 is

scale forming, and a

saturation below 0.3 is

corrosive.

The

susceptibility of

metal to

corrosion is as

follows (most

susceptible to

least susceptible):

magnesium, zinc,

aluminum,

cadmium, mild

steel, cast iron,

stainless steel (active), lead-tin solder, lead, tin, brass, gun

metal, aluminum bronze, copper, copper-nickel alloy,

Monel, titanium, stainless steel (passive), silver, gold, and

platinum.

Water Conservation

How much attention should be paid to fixtures that just

drip a little bit of water or that just will not quite shut

off? At 30 drops per minute, you will lose and pay for

54 gallons per month. At 60 drops per minute, you will

lose and pay for 113 gallons per month. At 120 drops per

minute, you will lose and pay for 237 gallons per month.

This is only a small loss of water considering the 5 to

7 gallons per flush used by a properly functioning toilet.

If the toilet is not properly maintained, the loss of water

and its effect on the monthly water bill can be incredible.

Lower flow toilets have been mandated to save precious

and limited resources. Most pre-1992 toilets used up to

7 gallons per flush. Toilets have since evolved to use 5.5,

then 3.5, and now 1.6 gallons per flush. 

With the changes in the water usage laws in 1992, there

were many customer complaints, and plumbers were in the

bad position of installing products that nobody wanted to

use. New and updated products now work better than the

old water wasters. 

According to the EPA, in 2000, a typical U.S. family of

four spent approximately $820 every year on water and sewer

fees, plus another $230 in energy for heating water. In

many cities, according to the U.S. EPA, water and sewer

costs can be more than twice those amounts. Many people do

not realize how much money they can save by taking simple

steps to save water, and they do not know the cumulative

effects small changes can have on water resources and

environmental quality. Fixing a leaky faucet, toilet, or

lawn-watering system can reduce water consumption.

Changing to water-efficient plumbing fixtures and

appliances can result in major water and energy savings [9,10].

Healthy Housing Reference Manual 9-13

Figure 9.15. Janitor’s Sink

Figure 9.16. Common Y-trap

Figure 9.17. Hose Bib With Vacuum Breaker
Summer droughts remind many of the need to appreciate

clean water as an invaluable resource. As the U.S. population

increases, the need for clean water supplies continues to

grow dramatically and puts additional stress on our limited

water resources. We can all take steps to save and conserve

this valuable resource.

The EPA [11] suggests the following steps homeowners

should take right away to save water and money:

• Stop leaks!—Check indoor water-using

appliances and devices for leaks. Pay particular

attention to toilets that leak.

• Take showers—Showers use considerably less

water than do baths.

• Replace shower heads—Replacement shower

heads are available that reduce water use.

• Turn the water off when not needed—While

brushing your teeth, turn the water off until you

need to rinse.

• Replace your old toilet—The largest water user

inside the home is the toilet. If a home was built

before 1992 and the toilet has never been

replaced, it is very likely that it is not a waterefficient, 1.6 gallons-per-flush toilet. Choose a

replacement toilet carefully to ensure that what

you make up per individual flush, you do not lose

because you must flush more often.

• Replace your clothes washer—The second largest

water user in the home is the washing machine.

Energy Star-rated washers that also have a water

factor at or lower than 9.5 use 35%–50% less

water and 50% less energy per load. This saves

money on both water and energy bills.

• Plant the right plants with proper landscape

design and irrigation—Select plants that are

appropriate for the local climate. Having a 100%

turf lawn in a dry desert climate uses a significant

amount of water. Also, home owners should consider

the benefits of a more natural landscape or wildscape.

• Water plants only as needed—Most water wasted

in the garden is by watering when plants do not

need it or by not maintaining the irrigation system.

If manually watering, set a timer and move the

hose promptly. Make sure the irrigation controller

has a rain shutoff device and that it is

appropriately scheduled. Drip irrigation should be

considered where practical. Newer irrigation

systems have sensors to prevent watering while it

is raining.

Putting It All Together

These photographs, taken during construction of a home

by Habitat for Humanity, show various plumbing

elements discussed in this chapter.

9-14 Plumbing

A. 

Hot and cold copper water lines and drain, p-trap and vent,

and vent for the washer drain shown. When a house is

vacant for awhile, the P-trap should be filled with water to

prevent sewer gas from entering the home. Mineral oil added

to the water can slow the loss of fluid in the trap.

B. 

Hot and cold water pipes, soil pipe, and vent shown.
References

1. US Environmental Protection Agency. United

States Environmental Protection Agency guidance

from hotline compendium: lead ban.

Washington, DC: US Environmental Protection

Agency; 1988. Available from URL:

http://www.epa.gov/safewater/wsg/wsg_H19.pdf.

2. Uni-Bell PVC Pipe Association. Handbook of

PVC pipe design and construction. Dallas: UniBell PVC Pipe Association; 2001. Available from

URL: http://www.uni-bell.org/pubs/

handbook.pdf.

3. Occupational Safety and Health Administration.

Safety hazard information bulletin on the use of

polyvinyl chloride (PVC) pipe in above ground

installations. Washington, DC: Occupational

Safety and Health Administration; 1988.

http://www.osha.gov/dts/hib/hib_data/

hib19880520.html.

4. Copper Development Association. Copper in

your home: plumbing, heating, cooling. New

York: Copper Development Association; no date.

Available from URL: http://www.copper.org/

copperhome/PHC/phc_home.html.

5. Plastic Pipe and Fittings Association. Cross-linked

polyethylene. Glen Ellyn, IL: Plastic Pipe and

Fittings Association; no date. Available from

URL:

http://www.ppfahome.org/pex/historypex.html.

6. NAMCO. Determine the total fixture unit load.

Dallas: NAMCO; no date. Available from URL:

http://www.namco-div.com/booster/

sel%20criteria/fixtureload.htm.

7. Energy Efficiency and Renewable Energy

Clearinghouse. Demand (tankless or

instantaneous) water heaters. Merrifield, VA:

Energy Efficiency and Renewable Energy

Clearinghouse; no date. Available from URL:

http://www.toolbase.org/tertiaryT.asp?

DocumentID=3206&&&CategoryID=0.

8. Public Health-Seattle and King County. Public

health plumbing program: water supply fixture

units (WSFU) and minimum fixture branch pipe

sizes. Seattle, WA: Public Health-Seattle and King

E. 

Polyethylene water

service pipe entering

the home through the

concrete basement wall

shown. White plastic

adapter shown

between polyethylene

water service pipe and

3⁄4 inch copper water

line. A short distance

above the adapter is a

pressure reducing

valve. To the right of

water line is the 4-inch PVC pipe waste water line.

Healthy Housing Reference Manual 9-15

C. 

Vent for the sink and toilet, soil pipe, and cap for toilet

connection shown. A wax or plastic seal shaped like a donut

will be placed on the cap before bolting down the toilet.

D. 

Mixing and antiscald water flow contro, vent for fixture, hot

and cold water lines, and bathtub overflow shown. At this

point in construction, insulation might be considered for the

hot water lines. Water service and waste water line.
County; no date. Available from URL: http://

www.metrokc.gov/health/plumbing/wsfu.htm.

9. US Environmental Protection Agency. Developing

water system financial capacity. Washington, DC:

US Environmental Protection Agency; 2002.

Available from URL:

http://www.epa.gov/safewater/dwa/

electronic/presentations/pwsoper/fincapacity.pdf. 

10. US Environmental Protection Agency. Water and

wastewater pricing. Washington, DC: US

Environmental Protection Agency; no date.

Available from URL: http://www.epa.gov/water/

infrastructure/pricing/.

11. US Environmental Protection Agency. Using

water wisely in the home. Washington, DC: US

Environmental Protection Agency; 2002.

Available from URL:

http://www.epa.gov/owm/water-efficiency/

waterconservation_final.pdf. 

Additional Sources of Information

American Backflow Prevention Association. Available

from URL: http://www.abpa.org.

American Society of Plumbing Engineers. Available from

URL: http://aspe.org.

American Society of Sanitary Engineering. Available from

URL: http://www.asse-plumbing.org.

American Water Works Association. Available from URL:

http://www.awwa.org.

National Sanitation Foundation. Available from URL:

http://www. nsf.org/international.

Plumbing-Heating-Cooling Contractors Association.

Available from URL: http://www.phccweb.org.

Underwriters Laboratories Inc. Available from URL:

http://www.ul.com.

For more water conservation tips and energy saving ideas

for businesses, industries, and individuals, visit the EPA’s

Water-use Efficiency Program Web site

(http://www.epa.gov/owm/water-effic iency/index.htm).

9-16 Plumbing