Water Supply

Groundwork

Water service lines are typically copper, polyethylene, or rigid plastic. Care should be taken to avoid damage when laying pipe:

• Bury all water service lines below frost-depth.
• Clear trenches of sharp rocks.
• Provide continuous support (layer of soft dirt or sand) to prevent pipe from sagging or breaking when backfilled.
• Bed PVC water lines in 4 in. of sand or fine dirt.
• Keep the number of joints in trench to a minimum.
• Backfill around pipe with fines until the pipe is submerged 6 in.
• Do not backfill with heavy rock or cinder material that may promote corrosion. 

Water service lines may not be laid in the same trench as sewer lines unless they are separated by an elevation of at least 12 in. (some codes permit 10 in.). This means the sewer line will end up at least one foot below frostline. More typically, sewer and water lines are laid at the same depth in separate trenches spaced at least 5 ft. apart (Water Service Installation, below).

Install caution tape: Best practice calls for burying caution tape 12 in. below grade to alert future excavators to the presence of sewer and water service lines. This marking usually is color-coded — blue for water and green for sewer.

For information on subslab layout, see Structural Slabs.

Water service entry. Supply piping passing under a footing must have a clearance of at least 2 in. (See Figure: Drain Lines Near Footing in Groundwork).

Any supply piping passing through a foundation or footing must be sleeved with a pipe two sizes larger than the water line, allowing 1/2-in. clearance around the circumference of the supply line. This provides corrosion protection and prevents the water line from breaking if the foundation settles. Seal the sleeve with flexible foam to keep out the cold. In termite-prone regions, seal the outside with a flexible electrometric compound.

Lawn sprinkler systems that tap off a water service line must be protected by an approved backflow preventer (typically an atmospheric-type anti-siphon vacuum breaker). An atmospheric vacuum breaker must be at least 12” higher than the highest head in the system. If water pressure fails, this backflow prevention device will bleed air into the system rather than suck irrigation water back into the supply line. 

Turn the sprinkler run to rise 6 in. above grade after branching from the water service, and install a control valve. The backflow preventer must be located on the discharge side of the sprinkler control valve.

Figure: Water Service Installation

Water Wells

Rural houses often rely on a well. This type of water system contains a submersible pump in the well that feeds a pressure tank in the house (below).

Figure: Anatomy of a Well System

Pressure System Parts

Tank. An old pressure tank may not have a bladder as new tanks do. The bladder contains water, which prevents the air from dissolving into the water over time.

Shutoff valve. The main valve must be a full-flow valve, which allows water to flow unrestricted. Use a heavy-duty ball valve. Never use gate valves: They cause too many problems, as do cheap ball valves.

Pressure switches come set up for 20/40, 30/50, and 40/60. The lower figure is the cut-in pressure, and the higher figure is the cut-out pressure. But you can adjust to almost any pressure combination. Inside the pressure switch housing are two adjustment screws. Turning the nut on the tall screw shaft clockwise will increase the overall pressure at both the top end and the bottom end of the cycle.

Pipe to the pressure switch. Use a 1/4-in. ID (inside-diameter) pipe that takes the water from the big brass T and sends it to the pressure switch. Because this pipe has a small diameter, it can easily rust. Always use a 1/4x4-in. brass nipple for the connection; brass won’t corrode like galvanized pipe.

Water pressure gauge. Buy the best available. Inexpensive gauges have short life spans. 

Tank T. This is a specialty manifold for the many connections just before the tank. It includes ports for the pressure gauge, the pressure switch, a drain valve, and a pressure relief valve.

Well Piping

For wells less than 500 ft. deep, the best pipe to use is 1-in.-diameter polyethylene (black rolled plastic). The pipe should be rated for 160-pound pressure and must have “water service pipe” printed on it. For deep wells (at or around 500 ft.), use 200-pound rated pipe. 

Pipe clamps must be stainless-steel marine clamps, not hose clamps. Beware: Some clamps that claim to be all stainless have only a stainless band; the screw housing may not be stainless.

Well Pump

A submersible pump has two main parts. The top part is the pumping mechanism, called the pump head. The bottom part is the motor. Water is drawn in between the two. 

Pump capacity. A submersible pump head is no more than a bunch of little stacked impeller stages. The water gets whirled around in one and thrown to the next. Each little impeller raises the water pressure a small amount. The deeper the well, the more impellers needed to get the water out. However, the more impellers needed, the greater the “drag,” which requires increasing the horsepower of the pump motor.

Typically, a 1/2-hp pump can pull water out of a well as deep as 140 ft., measured from the uppermost point in the system to the pump. The pump is normally placed 20 ft. off the bottom to allow for sediment to settle out. 

The most common pumps are rated at 7 to 10 gallons per minute. A faster pump is unnecessary unless the well has a very fast recharge rate. When installing a higher-rated pump, make sure it’s matched with a larger pressure tank or install a series of tanks.

Wiring a pump. A two-wire system is less expensive (there’s less wire) and simpler to install than a three-wire system. Three-wire systems require switching both the run and start wires.

Use special submersible pump wire from the pump to the top of the wellhead; it is listed just for this purpose. However, from the wellhead to the house (all the way to the pressure switch), you must use UF wire. 

The splice between the submersible pump wire and the submersible pump must work under water. To do this, use a submersible splice kit, crimping the wires together and applying a heat-shrink sleeve over it to make the connection watertight.

Water Supply Materials

The 2003 International Residential Code (IRC) allows for a wide range of piping materials, but local codes may vary. The following are generally accepted:

Copper Tube

Copper tube is available in a range of types, identifiable by color code on the piping (below). Only types K, L, and M are allowed by code for water service and distribution in homes. Type M, while accepted, is widely considered too thin.

Polyethylene Pipe

Polyethylene pipe may be used for cold-water service — from a well pump to a water pressure tank or straight to a municipal main valve in a crawlspace.

Ordinary polyethylene is not approved for distribution in a house, as its maximum operating temperature is rated at 100°F, which is considered too low for most domestic hot-water systems.

A polyethylene water supply usually must terminate within 3 to 5 ft. of entering the house, depending on the codes. Whether the crawlspace is considered part of the building is up to the inspector. No tees are permitted in a polyethylene supply line until after it hits the main valve and transitions to the in-house distribution piping.

Cross-Linked Polyethylene (PEX)

Lightweight, tough, and flexible, cross-linked polyethylene (PEX) is increasingly used for water distribution in homes. It’s ideal for subslab installations and retrofits, and PEX tubing often allows for better flow rates. But the plumber must have the tools and expertise to work with it.

PEX systems can be used as parallel distribution — frequently called a “home run piping system” — consisting of a central manifold with individual tubes running to each fixture outlet (below).

Figure: Piping Manifolds

CPVC, PVC, and ABS

ABS and PVC are not permitted for water distribution pipe. They can only be used for service pipe. Only CPVC is rated for hot water service (maximum operating temperature of 180°F).

While CPVC is typically the most economical, it is the least reliable. Of the piping materials allowed by code, it has the least resistance to freezing. It is the least durable, and extra care should be taken in trenches to fully support the entire length with sand. Also, plastic distribution systems tend to be noisy when running through living areas.

Polybutylene

Though common for water supply and distribution up until 1995, this gray or blue plastic piping is no longer manufactured. It is believed that oxidants in the water cause piping to deteriorate, a situation that has led to massive lawsuits. Any existing PB piping in a home should be replaced.

Galvanized Steel

Galvanized steel pipe — Standard (Schedule 40), Extra Strong (Schedule 80), and Double Extra Strong (Schedule 160) — is accepted by the IRC. Never use black iron pipe for water lines, as it rusts quickly.

Sizing Supply Lines

Water supply lines must be properly sized to ensure adequate pressure to each fixture, even at the end of a long pipe run.

Sizing Individual Feeds

Most codes stipulate a minimum pipe diameter for each type of fixture; in almost all cases, that minimum is 1/2 inch (Minimum Sizes of Fixture Feeds, below). This applies to bathtubs with and without showers, toilets, kitchen sinks, dishwashers, and washing machines. Lavatories and bidets can usually be supplied by 3/8-in. lines, though it never hurts to use a 1/2-in. line.

Figure: Minimum Sizes of Fixture Feeds

Exceptions to the code’s sizing requirements are often made for distribution lines that run from a manifold (see Sizing Manifold Systems, below).

Sizing Service Lines

As supply lines branch to serve multiple fixtures, the diameter of each branch must be large enough to provide a sufficient supply of water for all its fixtures.

The sizes of service and distribution lines for most houses can be calculated using the fixture-unit method. To use this method, identify the following:

• the static water pressure of the system;
• the actual water pressure at the farthest fixture;
• the developed length of the piping;
• each fixture’s water load, expressed in supply fixture units.

Once these figures are gathered, the size of a water meter or main service line can be calculated by adding up the fixture units for all the fixtures in the house and tallying the developed length of the pipe running to the farthest fixture. The appropriate pipe diameter can then be chosen within a specific pressure range from the table in Minimum Size of Water Meters, Mains, and Distribution Piping, below. Sample calculations to determine the adjusted pressure, developed length, and total fixture unit value required to determine the size of the water service size are shown in Sizing Water Supply Pipes, below. Water pressure, developed length, and fixture units may affect the size of supply lines, as detailed below.

Caution. Many local codes have specific requirements that overrule sizing calculations. Be sure to check with an inspector before making a final determination.

Water Pressure

There are two kinds of water pressure: static pressure, which is measured when no water is flowing, and dynamic pressure, which is measured when water is flowing. Both the dynamic and the static pressure measured at a fixture are likely to be less than the static pressure measured at the meter or pressure tank. The drop in pressure is due to friction (as water flows through equipment, pipe, and fittings) and raising the water to a higher elevation.

System pressure. Most codes require residential static water pressure to be between 40 and 80 psi. The IRC requires a minimum of 40 psi. In areas where the municipal pressure is too low, the solution is to install a booster pump and pressure tank.

Pressure testing. When sizing the diameter of pipe runs, static pressure can be determined by measuring it with a pressure gauge just after the meter and pressure-reducing valve, or by contacting the local utility to ask what pressure is typical in the neighborhood. Where pressure varies, use the lowest value provided. (For example, on a rural system, the static pressure will vary between the cut-in and cut-out settings on the pressure switch controlling the pump — typically 45 to 60 psi. To size the pipe, use the minimum pressure of 45 psi.)

Actual pressure at fixtures. Some types of equipment, including water meters, backflow preventers, water filters, and water softeners, introduce friction that results in dynamic pressure loss. Contact the manufacturer of any such equipment to obtain pressure-loss information, and use this information to adjust the available water pressure downward (for an example of this adjustment, see Sizing Water Supply Pipes, below).

Even when no water is flowing, the pressure on the top floor of a multistory building will be less than the pressure in the basement. This type of pressure loss is called the static pressure loss, and supply pipes need to be reduced to account for it.

The International Plumbing Code specifies that for every foot of increase in elevation, the assumed pressure should be reduced by 0.433 psi. (Other codes may use lower adjustment factors, so be sure to check locally.)

So, for example, if the service pressure is 60 psi in the basement and the highest fixture is located 20 ft. higher than the water meter, the reduction in pressure will be 20 ft. multiplied by 0.433 psi, or 8.66 psi. This will drop the effective pressure down to 50 psi — the design pressure to use for sizing the pipes for the entire building.

Developed Length

It takes more pressure to push water through long narrow pipes than short fat pipes. Determine the length of the longest pipe in the house before choosing a diameter from the table in Minimum Size of Water Meters, Mains, and Distribution Piping, below. The developed length of a home’s supply pipe is usually defined as the distance from the water source (the water meter or pressure tank) to the most remote fixture.

The IRC requires that the pipe length measurement be multiplied by 1.2 to account for pressure loss due to fittings.

Figure: Minimum Size of Water Meters, Mains, and Distribution Piping

Fixture Units

Fixture-unit numbers don’t measure anything; the scale is used to compare the relative water requirements of different fixtures (Water Supply Fixture-Unit Values, below).

To size the main water supply for a house, add up all of the supply fixture units on the system, including hose bibbs and the lawn sprinkler system.

To size branch lines to a group of fixtures, add up the total fixture units being served by the particular branch line.

Figure: Water Supply Fixture-Unit Values

Sizing Branch Lines

Branch lines can be sized the same way as service lines (below), but include only the fixture units on a particular branch line. As a rule of thumb, the pipe diameter can drop down to 1/2 in. when there are only two fixtures remaining on a branch line.

Figure: Sizing Water Supply Pipes

Sizing Manifold Systems

In a parallel water-distribution system, such as a PEX system, the home-run is sized by the water demand of all the fixtures on the system in gallons per minute, not by fixture-unit values.

Sizing the manifold supply. To determine the size of the pipe supplying the manifold, add up the flow rates shown in Design Flow Rates of Residential Fixtures, below, for all the fixtures on the system. Once the total flow rate is known, consult the Manifold Sizing table, below.

Sizing distribution runs. Most manifold systems have individual tubing runs between the manifold and each fixture. The IRC allows a minimum size of 3/8 in. for distribution lines in a manifold system, though some toilets, whirlpools and other fixtures may require larger supply lines (as specified by the manufacturer).

Figure: Design Flow Rates of Residential Fixtures

Figure: Manifold Sizing

Supply Line Installation

Pipe Support

All plumbing lines running horizontally and vertically inside a building must be supported at intervals with hangers. Maximum distances between supports are shown below.

Figure: Supply Pipe Support

Plumbing Requirements for Domestic Hot Water

All water heaters must be protected by a combination temperature and pressure (T&P) relief valve.

• The T&P relief valve must be located within the top 6 in. of the water heater, with a drainpipe (copper, steel, or CPVC only) running down the tank to within 6 in. of the floor.
• No reducers may be used on the T&P drain.
• By code, the valve setting must not be greater than 150 psi and 210°F.

A full-open shutoff valve is required on the feed side of every water heater. In addition, unions should be located within 12 in. to allow the heater to be disconnected from the water service and distribution system for maintenance and repair. Both the cold inlet and hot outlet must be insulated within 5 ft. of the water heater. The figure below shows the recommended water tank capacity per number of bedrooms in a house.

Water Heater Location

It’s always a good idea, if possible, to keep the water heater near the bathroom to minimize heat loss.

Water heaters cannot sit on the ground (including a dirt basement). In these cases they must sit on a minimum 3-in. concrete pad.

In garages, areas open to a garage, or anywhere flammables are stored, the ignition source must be elevated at least 18 in. above the floor. In addition, it must be protected from vehicle impact by a framed wall or concrete piling.

In seismic zones, water heater tanks must be secured by steel straps in the upper and lower third of their height. The strap must resist a horizontal force equal to at least 1/3 the operating weight of the water heater (or according to the manufacturer).