Water Bill Triples in a Four-Flat Building
A four-flat, single-meter apartment building consumed 38 to 42 kL per month for three years. The latest bill shows 96 kL. All four families were away for ten days during that month, yet consumption during those ten days was 11 kL. There is a damp patch of about 1 m² on the outside wall, 300 mm above ground level, below the first-floor bathroom. It is cool and continuously wet even in dry weather, has no smell, and the paint is blistering. The owner has already broken open the bathroom floor around the floor trap and found nothing. The water meter is at the gate, 12 m from the building, and all taps and float valves in the building can be closed from one main valve inside the compound.
1. Describe the test you would perform at the meter, step by step, and state what each result would prove.
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- Confirm there is no draw: shut every tap, close the tank float valve so the tank cannot refill, and inform the occupants.
- Read the meter and note the smallest dial, which usually moves for 0.1 L or 1 L.
- Close the main valve inside the compound and watch for 15 minutes. If the meter stops, the leak is downstream of the valve, inside the building. If it keeps moving, the leak is on the 12 m service line between the meter and the valve.
- Reopen the valve, isolate one section at a time - tank inlet, first-floor riser, each flat - and watch the meter after each isolation. The section that stops the meter contains the leak.
- Run a minimum night-flow test between 2 and 4 a.m., when draw is near zero, and record the reading over 30 minutes. A steady movement of about 0.5 L/min or more with everything closed confirms a leak. The 11 kL in ten unoccupied days works out at 1,100 L/day, roughly 0.76 L/min - small and continuous, which points to a pinhole or a cracked joint rather than a burst pipe.
2. Decide whether the leak is on the supply side or the drainage side, and justify your decision from the symptoms.
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The leak is on the supply side. Three symptoms decide it:
- Water is consumed while nobody is at home. A drainage leak does not pass through the water meter, so 11 kL in ten empty days can only come from the pressurised supply.
- The wall is continuously wet even in dry weather. A drain leaks only when water is used and dries between uses; a supply leak runs 24 hours.
- The patch is cool, clear and has no smell. Soil water from a drain carries soap, grey water and sewer smell, and would stain and smell. The dug floor trap found nothing because the problem is not in the drain at all; the bathroom floor was the wrong place to look. The location, below the first-floor bathroom on the outside wall, suggests the concealed riser or the branch to that bathroom, which is consistent with a small continuous loss.
3. State how you would locate and repair the leak, keeping breaking of the load-bearing wall to a minimum, and how you would prove the repair.
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Locate: close the branch valve to that bathroom, drain and dry the patch, and see whether it stays dry. Then isolate the riser section and apply a low air pressure of about 3 bar with soap solution at joints, or use a moisture meter to map the damp area and a sounding rod at night to hear the escape. Trace the pipe route before cutting. Repair: open a neat 300 × 300 mm patch at the lowest moisture reading rather than stripping the whole wall; avoid chasing a load-bearing wall horizontally and keep any chase vertical and shallow. If the pipe is GI, cut out the corroded length and replace it with 25 mm CPVC or MDPE using compression or mechanical couplers, properly bracketed; do not simply clamp a pinhole, because GI corrodes from inside and will fail again nearby. Prove it: pressure-test the repaired section at 1.5 times working pressure for one hour with no drop, flush and chlorinate, then take meter readings before and after over a full day with normal occupancy to show the consumption has fallen back towards 40 kL per month. Photograph the repair and record it in the maintenance file.