Water Supply and Drainage Systems
Water Supply and Drainage Systems covers how potable water reaches fixtures and how soil and waste leave the building. The exam tests storage sizing, distribution arrangements, trap seals, venting and drainage gradients.
Supply arrangements
Direct supply feeds from the main; indirect supply fills an overhead tank and feeds by gravity. Include a float valve, isolation valve, water meter where required, and a vented overflow. Size the tank from occupancy × litres per capita per day (lpcd), plus cleaning and reserve allowance.
Drainage
Separate soil (WC) and waste (sink/basin) where required, or use a one-pipe system with venting. Every fixture needs a trap; the water seal stops sewer gas. Vent pipes equalise pressure and prevent siphonage. Use inspection chambers at changes of direction and a septic tank plus soak pit where no sewer exists.
Worked example
A house has 4 occupants at 135 lpcd. Daily demand = 4 × 135 = 540 L. Add 20% for cleaning and reserve = 648 L. A 1,000 L overhead tank gives about one and a half days of storage; a 500 L tank would be marginal.
Traps
Connecting storm water to the sewer; omitting a vent and blaming the trap; using a flat drain line; sizing a tank only from the number of taps; and forgetting the overflow and access cover.