Water Supply and Distribution
Domain overview
Water Supply and Distribution tests sizing, pressure, materials, backflow protection, water heaters, and freeze protection. North Dakota's cold climate makes freeze protection and thermal expansion part of the daily code check, not an afterthought.
Core rules
- Size water piping by fixture units, developed length, and available pressure; a larger pipe is not automatically correct if the pressure is inadequate.
- Maintain the code minimum flowing pressure at the most remote fixture; account for elevation (about 0.43 psi per foot of rise) and friction loss.
- Protect the potable supply with an air gap or an approved backflow preventer at boilers, irrigation, chemical equipment, and hose bibbs where required.
- Water heaters need a temperature-and-pressure relief valve piped full size to a safe drain, not capped or reduced, and thermal expansion needs a place to go.
- Support pipe at code intervals, protect it from freezing, and use compatible materials and dielectric fittings at dissimilar metal joints.
Worked example
A house has 60 psi static pressure at the meter. The highest fixture is 30 feet above the meter, costing about 13 psi in elevation, and the calculated friction loss is 12 psi. The residual is 60 - 13 - 12 = 35 psi, which is above the usual 15 psi fixture minimum. If the friction loss were 35 psi, the residual would be 12 psi and the system would fail; the fix would be larger pipe, a pressure-boosting pump, or a shorter route.
Traps
Do not subtract only friction and forget elevation. Do not cap a T&P relief valve or run it uphill. Do not connect a hose bibb to a chemical sprayer without a vacuum breaker. Do not ignore thermal expansion on a closed system with a check valve or PRV.