Building Water Supply System: Intro

Home | FAQ | Finishing | Sump Pumps | Foundations

Main Parts of a Water Supply System

Plumbing codes require that a potable water supply be adequately furnished to all plumbing fixtures. The water supply system in a building carries cold and hot water through distribution pipes and delivers it to the plumbing fixtures. Schematic drawings of conventional residential and commercial systems are shown in Ills. 1 and 2. The water service line carries water from a district supply pipe to the building. The main parts of a typical water supply system include the following.

Building Supply: The building supply or water service is a large water supply pipe that carries potable water from the district or city water system or other water source to the building.

Water Meter: A water meter is required by most district water supply systems to measure and record the amount of water used. It may be placed in a meter box located in the ground near the street or in side the building.

Building Main: The building main is a large pipe that serves as the principal artery of the water supply system. It carries water through the building to the furthest riser. The building main is typically run (located) in a basement, in a ceiling, in a crawl space, or below the concrete floor slab.

Riser: A riser is a water supply pipe that extends vertically in the building at least one story and carries water to fixture branches.

It is typically connected to the building main and runs vertically in the walls or pipe chases.

Fixture Branch: A fixture branch is a water supply pipe that runs from the riser or main to the fixture being connected. In a water supply system, it's any part of a piping system other than a riser or main pipe. Fixture branch pipes supply the individual plumbing fixtures. A fixture branch is usually run in the floor or in the wall behind the fixtures.

Fixture Connection: A fixture connection runs from the fixture branch to the fixture, the terminal point of use in a plumbing system. A shut-off valve is typically located in the hot and cold water supply at the fixture connection.

ILL. 1 Basic parts of a residential rigid-pipe distribution configuration. Branch pipes follow a straight-line path.

ILL. 2 Basic parts of a commercial rigid-pipe distribution configuration. Note the common plumbing chase.

General Water Distribution System Layout

The water service pipe is an underground pipe that's typically called a lateral. It extends from the underground street main that's part of a district or city water system, and delivers pressurized potable water to a building plumbing system. The water service lateral is connected to a water meter that measures consumption. The water meter is typically located in an underground curb box located in the building's front yard or is located in the building interior, in which case it's connected to a remote readout on the exterior of the building, which allows easy access for meter readings. If the building plumbing system is served by a well, a water meter is not needed unless monitoring of consumption is required. A water service shut off valve is typically located at the meter location.

As the building supply piping enters the building, pipes split off to supply water to hose bibbs, the irrigation system, and any industrial process equipment using water that does not need to be heated. A building shut-off valve is typically located at this location. If pressure available from the water service is too high, a pressure-reducing valve or pressure-reducing arrangement drops the water pressure to an acceptable level.

If water softening or treatment is desired in the building, water is passed through a softening or treatment device before the water is distributed to the building. Water softening or treatment is done after irrigation water and /or water for process equipment is removed. Once the water supply main passes through the softening or treatment device (if used), the main pipe splits to provide water to a water heater or water heating system that generates hot water before it's distributed.

A fixture connection links the hot or cold water branch to the fixture, the terminal point of use in a plumbing system. A shut-off valve is typically located in the hot and cold water supply at the fixture connection. Air chambers are installed as close as possible to the fixture valves or faucet and at the end of long runs of pipe to reduce water hammer.

In a conventional rigid-pipe water distribution method, fixture branches extend from a riser or main to the individual fixture being connected. A fixture branch is usually run in the floor or in the wall behind the fixtures. In the innovative homerun water distribution method, individual branches begin at a main manifold located in a utility room or basement, usually near the water service. Individual hot and cold water branches extend uninterrupted to each plumbing fixture or a fixture group. The distribution configuration methods are described in the following.

IMG. 1 Rough-in of a residential service line passing through a foundation wall.

IMG. 2 A residential service line with a shut-off valve.

IMG. 3 A residential service line with an interior water meter, shut-off valve (above meter), and pressure-reducing valve (below meter).

IMG. 4 A wall-mounted exterior water meter.

IMG. 5 An underground curb box ready for water meter installation.

IMG. 3 A residential service line with an interior water meter, shut-off valve (above meter), and pressure-reducing valve (below meter).

IMG. 4 A wall-mounted exterior water meter.

IMG. 5 An underground curb box ready for water meter installation.

IMG. 10 The rough-in connection for a showerhead. IMG. 13 A rough-in of fixture branches and drain for a laundry connection. IMG. 7 Fixture branches connecting to a bathtub.

IMG. 11 A rough-in of fixture branches for a bathtub (no showerhead).

IMG. 14 A finished laundry connection. IMG. 8 A front side view of branches connecting to a bathtub and showerhead.

IMG. 15 A rough-in of fixture branches for a group of lavatories in a public restroom. IMG. 16 Hot and cold water supply fixture connections. IMG. 17 Sealed openings to prevent flanking of sound from a bathroom above.

Rigid-Pipe Distribution Configuration

In the conventional rigid-pipe distribution configuration, the hot and cold water distribution pipes are installed parallel to one another as they convey hot and cold water to risers and branch pipes. Running pipes parallel with building walls and floors arrange pipes in an organized manner. Hot and cold pipes should be spaced at least 6 in (150 mm) apart or have insulation placed between them to prevent heat interchange. In top-quality work, both pipes should be insulated so that hot water pipes minimize heat loss and cold water pipes prevent surface condensation. Schematics of this system are shown in Ills. 1 and 2. Imgs. 1 through 17 show components of the rigid-pipe water distribution system.

A branch supplying water to two or more fixtures is called a zone. A zone can supply one or many fixtures on one floor or on a few floors. Fixtures are typically located in clusters called groups. For example, in a commercial building or school, restrooms for men and women are grouped together with fixtures arranged against a common plumbing chase;

that is, fixtures back up on both sides of walls enclosing the plumbing chase. Water fountains are also located in the area of the restrooms. Likewise, a set of showerheads is located on a common chase or wall. A group arrangement allows several fixtures to be served by the same water main or branch.

For efficiency and convenience, risers and chases should be located near plumbing groups.

In wood and light-gauge steel frame construction, holes are drilled or cut to allow the passage of the pipes. Holes are located in the center of the framing members to avoid nails or screws penetrating the pipe and to minimize structural damage in load-bearing members. Metal plates cover pipes in wood framing when the pipe surface comes too close to the surface of the framing and there is a possibility of nail or screw penetration. There are times when the width of a wall needs to be in creased to allow for pipes running horizontally to pass by drainage pipes (or other pipes) running vertically. These walls of increased thickness are called plumbing walls.

The spaces in the open web of wood or steel truss construction (e.g., wood trusses and steel joists) make it easier to run piping through these structural members without affecting their structural integrity. It is sometimes difficult to feed long lengths of pipe through closely spaced trusses or open web joists after they are installed. A point of difficulty also exists where pipe encounters some other large pipe or ductwork going in the opposite direction. This necessitates coordination with the subcontractors erecting the trusses and installing the heating, air conditioning, or ventilating ductwork.

On projects with concrete walls and ceilings, it's typically necessary to provide sleeves (holes) in the concrete for the pipes to pass through to get from space to space. It will also be necessary to provide inserts and hangers to support the pipes.

Pipes placed below poured concrete slabs and in concrete-steel composite decking must be placed before the concrete is poured. Typically, both the water supply and drainage pipes are laid out next to each other, because they go to the same areas of the project. Many times, they are planned so they will come up in a partition, so accurate placement of piping is crucial. Tub, shower, and water closet piping will need to be placed in the exact location where the fixture is to go. All piping must be carefully located and the system checked for leaks before the concrete is poured because any relocation or repairs of pipes would be costly.

In multistory buildings, risers are pipes that carry water vertically through walls or through enclosures called chases. A chase is a vertical opening through a floor or several floors that's enclosed with walls between floors. A chase can enclose piping only or it can enclose electrical wiring and /or mechanical system ducting and /or pipes that run vertically from floor to floor through the building.

Pipe tunnels may be used on large projects to provide concealed space for the passage of mechanicals at ground level and from building to building. Hangers from the top or side of the tunnel are used to support the pipes. Access may be from either end of the tunnel, or access floors may be provided.

Readily accessible valves used to close off the water sup ply to a fixture, appliance, or system are called shut-off valves. A shut-off valve is required on the discharge side of the water meter. When more than one building is served by a single water service line, a shut-off valve must be installed at each building. A readily accessible shut-off valve must be installed on the cold water supply line feeding a water heater in the proximity of the appliance. In multifamily installations, single or multiple shut off valves must be installed in each dwelling unit so water to the unit can be shut off without interrupting the supply to other units.

Valves must be accessible in the dwelling unit they control.

ILL. 3 Basic parts of a homerun (manifold) distribution configuration. Hot and cold water lines dedicated to each fixture originate at individual ports in the manifold and extend to the individual fixture.

IMG. 18 The manifold of a homerun water supply distribution configuration. Water enters the manifold at the bottom. The pipes at the top of the manifold serve and return from the water heater. Flexible pipes (cold water on the right and hot water on the left) run to individual fixtures.

IMG. 19 A clearly marked set of hot water (left) and cold water (right) ports on a manifold.

IMG. 21 Water lines dedicated to each fixture run from the manifold to the individual fixture. Because of the flexibility of PEX pipe, fittings are not needed except at the start (manifold port) and end (fitting at fixture).

IMG. 22 The backside of the terminating fitting at the end of runs of PEX pipe in the homerun water supply distribution configuration.

IMG. 20 A close-up of the manifold of a homerun water supply distribution configuration shown in the previous photograph. A water line dedicated to each fixture originates at a port in the manifold and extends to the individual fixture. A valve at each port can shut off water to the individual fixture.

ILL. 4 An upfeed plumbing system supply relies on street pressure to drive water flow.

Homerun (Manifold) Distribution Configuration

A homerun or manifold distribution configuration consists of a plastic or metal plumbing manifold and flexible plastic piping.

A schematic of this system is shown in Ill. 3. The manifold serves as a common location from which all the plumbing fixtures are supplied. Manifolds have two separate chambers:

the cold water chamber is supplied from the main water supply line and the hot water chamber is fed from the water heater. A water line dedicated to each fixture originates at a port in the manifold and extends to the individual fixture, so fewer fittings are required. Some manifolds offer shut-off valves so each fixture can be turned off individually at the manifold. In a hybrid configuration, termination or secondary manifolds may feed the plumbing requirements for a room or set of rooms and re duce the number of fittings required in the plumbing system.

Imgs. 18 through 22 show components of the homerun (manifold) water distribution system.

Homerun configurations typically use cross-linked poly ethylene (PEX) or composite PEX-AL-PEX piping, which is suitable for cold and hot water use. Because of the flexibility of PEX, there is less of a need for piping tees and elbows. With one fitting needed at the manifold and a second transition fit ting at the fixture, a single run is made from the manifold to the fixture. As a result, homerun configurations can be installed more quickly than rigid plumbing. Fittings and couplings are available for unique situations, such as creating changes in direction that are tighter than the minimum bend radius allowable for the piping. The homerun configuration requires much more pipe than the rigid configuration, but the plastic pipe used is much less expensive than the metal (copper) pipe used in the rigid-pipe configuration. As a result, the home run configuration is typically cheaper.

Homerun configurations equalize pressure, which allows several fixtures to be operated simultaneously without drastic changes in pressure or temperature. Because each fixture has its own supply line, the size of the pipe can be adjusted for a fixture's specific use. In addition, for some fixtures, PEX piping can be downsized (usually 1/8 in diameter smaller) in comparison to a conventional rigid-piping configuration. A smaller diameter means that hot water arrives at fixtures faster, and less hot water is left standing in pipes after a fixture is operated.

Upfeed and Downfeed Distribution

Two basic types of water supply distribution systems are used in buildings: the upfeed (or upflow) system and the downfeed (or downflow) systems. See Ills. 4 and 5. Variations of these distribution systems are described in the paragraphs that follow.

In a conventional upfeed system, water pressure from the water supply main is relied on to drive water flow through the system. Water pressure in building water supply mains typically ranges from 40 to 80 psi (275 to 550 kPa), with 80 psi (550 kPa) considered the upper limit for most systems plumbed with metal pipe and 40 psi the upper limit for plastic pipe.

(Note: psi is an abbreviation for lb/in^2.) This available pressure places limits on how far water can be driven upward in a plumbing system. Part of the available pressure is expended in friction losses as the water passes through the meter and the various pipes and fittings; and part of the pressure is expended to overcome gravity, which is the pressure required to push the weight of water upward vertically (up the riser). Additionally, there must be sufficient pressure left at the remote fixture to drive flow of water through the fixture.

It takes 0.433 psi to push water up 1 ft vertically or, in the SI (metric) system, 9.8 kPa to push water up 1 m vertically.

Conversely, a 1.0 psi pressure can push water upward 2.31 ft vertically or, in the SI (metric) system, 1 kPa to push water up 0.144 m vertically. (This concept is further discussed later in this section.) Pushing water up 20 ft (6.1 m) vertically requires a pressure at the base of the riser of at least 8.68 psi (42 kPa), because 20 · 0.433 psi _ 8.68 psi.

ILL. 5 A downfeed plumbing system supply is needed to provide adequate pressure on upper floors. It is usually combined with an upfeed system that provides water to the lower floors.

If a pressure of 80 psi (550 kPa) is available at the base of a plumbing system riser, the maximum height water can rise vertically is 185 ft (56.5 m), because 80 psi · 2.31 ft _ 185 ft.

Depending on the exact floor-to-floor height, a pressure of 80 psi (550 kPa) would drive water about 15 stories, but only if there were no friction losses or fixture operation pressures to consider. When friction loss and fixture operation are taken into account, practical design limitations typically establish about 60 ft (18 m) as the standard maximum height and 40 ft (12 m) as the preferred maximum height. This limits a conventional upfeed system to buildings with a height of about 5 stories.

In tall buildings, water must be supplied through a pumped upfeed distribution system. A pumped upfeed system is one in which water entering the building flows through pumps that maintain adequate water pressure throughout the structure sufficient to operate any plumbing fixture. In a high rise building (e.g., 50 stories), water enters one or more pumps where its pressure is boosted to pressures of 150 to 250 psi (1000 to 1700 kPa) or more. A vertical riser carries this high pressure water to fixtures at the top of the building. Such a pres sure in the distribution system is too great to use in plumbing fixtures (e.g., lavatories and water closets). For this reason, at several zones water is removed from the vertical riser, reduced in pressure at pressure-reducing stations and distributed to the fixtures in that zone. The pressure-reducing stations, which are located about every 10 floors, monitor and adjust for any variation in pressure. This ensures that water available to plumbing fixtures is always kept under a constant pressure.

In buildings that can't be adequately serviced to the top floor by an upfeed system, water is pumped to elevated storage tanks in, or on, the building, and the water is fed down into the building by gravity. This gravity system, fed from the upper stories to the lower, is called a downfeed distribution system.

Water entering the building flows through pumps that develop sufficient water pressure to drive water to storage tanks serving zones of about 10 floors each. To develop adequate pressure, the storage tanks are placed above the zones that they serve.

TBL. 1 REQUIRED RESIDUAL PRESSURE FOR DIFFERENT FIXTURE TYPES. RESIDUAL PRESSURE IS THE PRESSURE IN THE PIPE AT THE ENTRANCE TO THE PARTICULAR FIXTURE.

Fixture: Ordinary basin faucet Self-closing basin faucet Sink faucet-3/8 in Sink faucet-1/2 in Bathtub faucet Laundry tub cock -1/2 in Shower Water closet Urinal (lush valve); Garden hose, 50 ft, and hose bibb/sill cock.


















Top of Page Home Prev: Next: Water Pressure Considerations Related Articles

Updated: Tuesday, February 21, 2012 11:43