Prevention of Backflow
All water-supply and distribution piping must be designed so there is no possibility of backflow at any time. The minimum code-required air gap (distance between the fixture outlet and the flood-level rim of the receptacle) should be maintained at all times. Domestic water systems that are subject to back siphonage or backflow should be provided with approved vacuum breakers or backflow preventers (Art. 14.3). Before any potable-water piping is put into use, it must be disinfected using a procedure approved by the local code authorities.
Pipe Materials
Pipes and tubing for water distribution may be made of copper, brass, polyvinyl chloride (PVC), polybutylene, ductile iron, or galvanized steel, if they are approved by the local code. When materials for potable-water piping are being selected, care should be taken to ensure that there is no possibility of chemical action or any other action that might cause a toxic condition.
Fittings
These are used to change the direction of water flow (because it usually is not practical to bend pipe in the field), to make connections between pipes, and to plug openings in pipes or close off the terminal of a pipe. In a water-supply system, fittings and joints must be capable of containing pressurized water flow. Fittings should be of comparable pressure rating and of quality equal to that of the pipes to which they are connected.
Standard fittings are available and generally may be specified by reference to an American National Standards Institute or a federal specification. Fitting sizes indicate the diameters of the pipes to which they connect. For threaded fittings, the location of the thread should be specified: A thread on the outside of a pipe is called a male thread, whereas an internal thread is known as a female thread.
Ductile-iron pipe is generally available with push-on mechanical joint or flanged fittings. Brass or bronze fittings for copper or brass pipe also may be flanged or threaded. Flanges are held together with bolts. In some cases, to make connections watertight, a gasket may be placed between flanges, whereas in other cases, the flanges may be machine-faced. Threaded fittings often are made watertight by coating the threads with an approved pipe compound or by wrapping the threads with teflon tape before the fittings are screwed onto the pipe.
