Installation of Water Supply, Sanitary, and Drainage Piping Systems
Water supply, sanitary and drainage installation
This domain tests installation of pressure water lines and gravity drainage and vent systems, including slope, support, testing and backflow protection. Exam items often ask you to calculate fall, choose a fitting or identify a code violation.
Core rules
- Water supply: install valves at fixtures and isolation points, protect against backflow, provide air chambers or arrestors where required, support at specified spacing and test hydrostatically before closing walls.
- Drainage: maintain continuous fall in the direction of flow. Common rules are 1/4 in per foot, about 2%, for 3 in and smaller, and 1/8 in per foot, about 1%, for 4 in and larger where the code or specification permits. Confirm the approved slope.
- Vent every trap; keep trap seals at the required depth, commonly 50-100 mm. Provide cleanouts at changes of direction and at the base of stacks as specified.
- Use drainage fittings such as wyes and 45-degree bends for horizontal changes; do not use a sanitary tee where the code requires a wye.
- Bed and compact drainage pipe properly; provide thrust blocks or restrained joints where required.
- Keep water and sewer lines at the required separation; never rely on colour alone to identify a line.
Worked example
A 4 in PVC horizontal drain runs 18 m at an approved slope of 1%. Reasoning: fall = 18 m × 0.01 = 0.18 m. If the upstream invert is at −0.30 m, the downstream invert is −0.30 − 0.18 = −0.48 m. Set the pipe supports so the fall is continuous, install cleanouts and vents as shown, and test before backfilling.
Traps
Negative or flat slope, missing vents, gluing joints before inspection, no cleanout at a direction change, and using the wrong fitting are common. A drain that drains by eye can still fail an air test or leave a trap seal siphoned.