Water supply and plumbing fixtures

Plumbing is the oldest building service and still one of the most regulated, because a plumbing failure can make people sick. A building's water supply system brings safe drinking water from the municipal main or a well, measures it, protects it from contamination, distributes it at a usable pressure, heats part of it, and delivers it to fixtures. Lesson 3 follows the water back out through the drainage system. This lesson covers the supply side: the service and meter, pressure, materials, backflow protection, hot water, fixtures and the way designers size pipes.

For the construction manager, water supply work is mostly rough-in hidden in walls and ceilings, tested under pressure, inspected, then covered. Mistakes are expensive to find later. Understanding the system helps you sequence the work, organize pressure tests and inspections, review submittals for fixtures and water heaters, and recognize when a field change might affect water quality or code compliance.

The water service and meter

The supply begins at the municipal water main in the street. A service pipe runs from the main, through a curb stop or service valve at the property line, to the building, where it enters below the frost line, passes through a main shut-off valve and a water meter, and then through a backflow preventer that stops building water from flowing back into the public system. Large buildings may have a separate fire service for sprinklers, often with its own backflow preventer and meter arrangement, as lesson 7 explains.

Frost depth varies widely across the United States, from almost nothing in the South to more than 5 feet in the northern states. Local codes and utility standards set the minimum cover for service pipes. Meter pits and service entries must be protected from freezing, and exposed piping in unheated spaces needs insulation and, sometimes, heat tracing.

The construction manager coordinates the service connection with the municipality or water utility, which usually performs or inspects the tap into the main and may have long waiting times for connection permits and meters. Temporary water for construction is a separate early arrangement, often through a hydrant meter.

Pressure: static, residual and the effect of height

Water pressure is what pushes water up through the building and out of fixtures. Static pressure is the pressure when no water is flowing; residual pressure is the pressure while water is flowing, which is lower because of friction. Each meter of height costs about 9.81 kPa (each foot costs about 0.433 psi), so upper floors of tall buildings receive less pressure than the ground floor.

Fixtures need a minimum flowing pressure to work well, typically around 100 to 140 kPa (15 to 20 psi) for ordinary fixtures and more for flush valves. Too much pressure is also a problem: it wastes water, wears out fixtures and causes noise and water hammer.

The plumbing codes require a pressure-reducing valve where static pressure exceeds 80 psi (IPC 604.8), so supply systems are often divided into pressure zones. Low pressure on upper floors is solved with booster pumps.

Piping materials

Water supply piping must be approved for potable water, which in practice means certified to NSF/ANSI 61 for health effects and, for lead content, NSF/ANSI 372. Common materials include:

• Copper tube (types K, L and M), joined by soldering, brazing or press fittings; durable, but costly and sensitive to aggressive water.
• Cross-linked polyethylene (PEX), flexible and fast to install with crimp or expansion fittings, widely used in residential and increasingly in commercial work.
• Chlorinated polyvinyl chloride (CPVC), solvent-welded, used for hot and cold water in some buildings.
• Stainless steel and ductile iron for larger mains and services; polypropylene (PP-R) in some commercial systems.

Under the federal Reduction of Lead in Drinking Water Act, effective in 2014, pipe, fittings and fixtures for potable water must contain no more than 0.25 percent lead by weighted average of wetted surfaces.

Material substitutions are a common source of submittal questions. A change from copper to PEX may be acceptable to the code and cheaper, but it can affect fire stopping, support spacing, thermal expansion and the owner's maintenance preferences, so it needs the engineer's approval.

Backflow and cross-connection control

A cross-connection is any link between the potable water system and a source of contamination: a hose in a mop sink, a boiler fill line, a chemical dispenser, an irrigation system or a fire sprinkler system. If pressure in the supply drops, for example during a main break or heavy fire flow, contaminated water can be siphoned back (back-siphonage) or pushed back by higher pressure (backpressure).

The defenses, from simplest to most protective, are:

• Air gaps, a physical space between the outlet and the flood level of the receptor; the most reliable protection.
• Atmospheric and pressure vacuum breakers, for back-siphonage on hose bibbs and irrigation.
• Double check valve assemblies, for low-hazard connections such as many fire sprinkler systems.
• Reduced pressure principle assemblies (RP or RPZ), for high-hazard connections such as boilers with chemical treatment, labs and medical equipment.

Backflow devices in the United States are certified to ASSE or AWWA standards and approved by programs such as the University of Southern California Foundation for Cross-Connection Control. Water utilities run cross-connection control programs under state drinking water rules, and testable devices must usually be tested by a certified tester at installation and annually.

Reduced pressure assemblies discharge water when they operate, so they need a floor drain or air gap nearby; this is a frequent coordination miss in mechanical rooms.

Hot water

Domestic hot water can be generated by storage tanks (gas or electric), tankless or instantaneous heaters, boilers with indirect tanks, or heat pump water heaters, which are increasingly required to meet energy targets. Large buildings use a recirculation loop so that hot water reaches distant fixtures quickly.

Temperature is a safety balance. Water must be stored hot enough to control Legionella bacteria, typically at least 60 °C (140 °F), but delivered cool enough to avoid scalding, typically no more than 49 °C (120 °F) at fixtures such as showers and lavatories, through thermostatic mixing valves. Building water management programs, guided by ASHRAE 188 in both countries, address Legionella risk in larger buildings.

Fixtures and fixture counts

The building code sets the minimum number of water closets, urinals, lavatories, drinking fountains and service sinks from the occupant load and the occupancy type, and requires accessible and, increasingly, universal washrooms. Water efficiency standards set maximum flow rates: for example, about 4.8 liters (1.28 gallons) per flush for high-efficiency toilets and about 1.9 liters per minute (0.5 gpm) for public lavatory faucets, though the exact limits depend on the code edition and the green building program.

Fixture counts in most of the United States come from IPC Table 2902.1 or the UPC, which set ratios by occupancy. For business (office) occupancies the IPC requires one water closet per 25 for the first 50 people and one per 50 for the rest, and one lavatory per 40 for the first 80 and one per 80 for the rest.

How pipes are sized

Pipe sizing is the engineer's job, but the method is worth understanding. Not every fixture runs at once, so designers estimate a probable peak demand. The traditional method assigns each fixture a number of water supply fixture units, adds them up, and converts the total to a design flow using Hunter's curve, then sizes each pipe so that velocity stays within limits (often around 1.5 to 2.4 m/s, or 5 to 8 ft/s) and pressure stays above fixture minimums. Newer methods, such as the Water Demand Calculator in Appendix M of the IPC and UPC, estimate peak demand from modern low-flow fixtures and often allow smaller pipes for dwellings.

Testing, disinfection and handover

Before concealment, water piping is pressure tested, commonly with water at the working pressure or at least 50 psi above it, or as the code and specification require (IPC 312.5 allows water or air tests for some materials). Before use, the system is flushed and disinfected under AWWA C651 or C652 practices and the plumbing code, and water samples are tested for bacteria.

The construction manager should schedule tests floor by floor, witness them with the inspector or engineer as required, record results, and keep disinfection reports for the closeout package. Newly built systems that sit unused before occupancy can develop stagnant water and Legionella risk, so flushing plans before turnover are increasingly part of commissioning.