Water Supply and Distribution
Pressure, flow, and sizing
Distribution is sized by water supply fixture units (wsfu) and developed length. Know the pressure rules: the code sets a minimum residual pressure at fixtures (roughly 8 psi flowing) and requires a pressure-reducing valve when static pressure exceeds 80 psi. Sizing tables assume a maximum velocity to limit noise and erosion, so a short run in small pipe is not automatically acceptable. Thermal expansion from a backflow preventer or PRV needs a closed system device.
Cross-connection control
Every point where nonpotable water could enter the potable system needs protection. The air gap is the only positive protection: the water inlet must sit at least twice the effective opening of the outlet above the flood level rim, and never less than 1 inch. Pressure vacuum breakers protect hose bibs; reduced-pressure zone assemblies protect high-hazard connections such as boilers with chemicals, irrigation, and commercial dishwashing.
Materials and installation
Copper, PEX, CPVC, and galvanized pipe are common in Michigan. Lead solder and lead-bearing materials are prohibited; fittings must be lead-free. Pipes must be protected from freezing - buried water service must be below local frost depth, which in Michigan is commonly 42 inches or deeper; verify with the local agency. Protect piping from freezing with heat trace, insulation, or drainage, and never bury a joint where it cannot be accessed for repair if the material prohibits it.
Worked example
A pressure gauge reads 62 psi at a basement main. Head in feet = psi × 2.31 = 62 × 2.31 ≈ 143 feet of head - how high the water would rise in an open standpipe.