Maintenance, Repair and Leak Detection
This domain tests fault finding, safe repair methods and the arithmetic of water loss.
Core rules and concepts
- Detect first, dig later. Check visible joints, then isolate sections with gate valves, then use a meter test: close every tap and fixture, note the meter reading, wait 15 minutes; movement means a leak on the live side.
- Other methods: listening for hiss at night, dye test in a cistern, smoke test on drains, pressure gauge drop test on a closed section, thermal or acoustic survey for buried mains.
- Repairs: change the washer or O-ring on a bib tap, repack the gland on a gate valve, re-thread and remake a joint, cut out and replace a damaged length, use a repair clamp on a pinhole, or epoxy putty on a weeping threaded joint after isolating and drying.
- Always isolate and drain before opening a joint; open the lowest tap to release pressure.
- Preventive maintenance: periodic inspection of tanks, float valves, pumps and supports; clean the sump; check the water seal in floor traps.
Worked example
A tap drips once a second. A drop is about 0.05 mL. Loss per day = 0.05 mL × 86,400 s = 4,320 mL ≈ 4.3 L/day, about 1,580 L a year. Reasoning: convert the drip rate into millilitres per second, multiply by seconds in a day, and convert to litres. This justifies a five-rupee washer.
Traps that cost marks
- Opening a joint while the line is still under pressure.
- Blaming the meter for movement caused by a leaking cistern float valve.
- Over-tightening an old cast iron fitting and cracking it.
- Replacing a washer without checking the seat.