Water Supply and Distribution
Sizing and pressure
Supply sizing starts with fixture units and the sizing tables, then is checked against available pressure. The code sets minimum residual pressures at fixtures, with flushometer-type fixtures needing considerably more than gravity-tank fixtures. A design that has enough pipe size but inadequate residual pressure fails. Velocity limits protect against noise and erosion, and excessive pressure at fixtures requires a regulator.
Protection of potable water
Backflow protection is graded by hazard. An air gap is the strongest protection; reduced-pressure-zone assemblies suit high-hazard connections; pressure vacuum breakers and atmospheric vacuum breakers cover lower-hazard, non-continuous connections; double check assemblies are for lower hazards. Testable assemblies must be tested and maintained. Devices must sit where they can be serviced, and no unprotected cross-connection may exist.
Installation and testing
Pipe supports are spaced by material and size, penetrations are sleeved and sealed, and buried lines are protected from frost and damage. Water piping is hydrostatically tested before being covered and before fixtures are connected - typically held at the code-specified test pressure for the specified duration, then inspected for leaks.
Worked example: a hose bibb in a commercial kitchen used to fill a mop sink needs an approved backflow device; a submerged inlet is a cross-connection regardless of how often it is used.
Trap to avoid: candidates over-specify protection (RPZ everywhere) or under-specify (a vacuum breaker on a continually pressurized, submerged line). Match the device to the hazard and to whether the connection is continuous.