Water system basics

Three kinds of water

Fresh water is the supply you intend to use. Grey water is wastewater from sinks and showers; local rules may classify kitchen waste differently. Black water contains toilet waste. Keep the systems physically separated and label every line and tank.

Pressure and flow

Pressure (PSI or bar) is the push available when water resists movement. Flow (GPM or L/min) is how much moves. A pump can advertise 55 PSI and 3 GPM, but the faucet may deliver less because pipe, fittings, filters and elevation create restriction.

Pipe size

A smaller inside diameter increases velocity and pressure loss. Long runs, elbows and restrictive cartridges add loss. The system must still stay below every component's maximum pressure.

Safe means more than no leaks

A safe system uses potable-rated materials, prevents backflow and contamination, controls pressure/temperature, avoids stagnant dead legs, can be cleaned and drained, and keeps wastewater away from fresh fittings and fill equipment.

Build rule

If you cannot reach it, isolate it, drain it and explain its pressure/temperature or water-quality job, it is not ready to hide behind a wall.

CHAPTER CHECK

• I can explain the purpose and failure mode of each item in this chapter. • I know which manufacturer limit or water-quality claim controls my choice. • I added the valve, access, drain, measurement or maintenance task to my drawing/checklist.