Water Supply and Distribution Systems
This domain covers how potable water reaches fixtures: sources, storage, pumping, pipe sizing, pressure, valves and backflow protection. Exam questions often ask you to compare direct and indirect supply, calculate pressure, or explain why a tap has poor flow.
System layout
In a direct system, mains pressure serves fixtures directly. In an indirect system, water is stored in an overhead tank and distributed by gravity, often with a pump for upper floors. Storage needs a covered tank, an air gap or approved backflow preventer, a float valve, overflow and cleaning access. Distribution should avoid dead legs, use isolation valves on branches, and provide a meter and strainer at entry.
Pressure and sizing
Pressure at a point equals the static head: p = ρgh. A 10 m head gives about 98 kPa, or roughly 1 bar, before friction losses. Size pipes using fixture units and the longest run; undersized mains cause poor pressure at peak demand. Fit water hammer arrestors near quick-closing valves and use pressure-reducing valves where static pressure is excessive.
Worked example
A tank outlet is 12 m above a first-floor tap. Static pressure = 1000 × 9.81 × 12 = 117,720 Pa ≈ 1.18 bar. If friction and valve losses total 0.30 bar, the tap sees about 0.88 bar. If the measured pressure is much lower, check tank level, strainer, valve position and pipe size before blaming the tap.
Traps that cost marks
Do not connect a potable line directly to a drain or irrigation line without an air gap or backflow preventer; do not leave dead legs that stagnate; do not size a branch from one fixture when it serves several; and do not ignore pressure loss through long runs, elbows and meters.