Quick answer
A sudden jump in your bill with no change in usage almost always means a silent leak, and the usual culprit is a toilet inlet valve trickling continuously into the bowl. An irrigation line, a slab leak, or a stuck pool auto-fill valve account for most of the rest. A silent toilet leak can waste thousands of litres a month while making no sound and leaving no visible water anywhere.
Common causes
- Silent toilet leak past a worn inlet valve or flush washer — by far the most common
- Buried irrigation line cracked and running underground
- Slab leak under tiles, showing up on the bill long before it shows on the floor
- Pool auto-fill valve stuck open and topping up continuously
- Geyser overflow discharging constantly from a failed pressure-control valve
- A municipal meter reading estimated rather than actual, which is worth ruling out first
What you can do now
- 1Read your meter, leave everything off for two hours, and read it again
- 2Dye-test every toilet with food colouring in the cistern
- 3Isolate the irrigation and the pool auto-fill, then repeat the meter test
- 4Check whether the geyser overflow pipe outside is running
- 5Compare the bill against the same month last year rather than last month, so seasonal irrigation does not mislead you
When to call a professional
If the meter advances during the isolation test, book a leak-detection call-out. Bring your last three bills and the meter readings you took — that record shortens the investigation considerably and helps if you intend to apply to the municipality for a leak adjustment, which many councils allow once a repair is documented.
Typical cost in Johannesburg
Leak detection R950–R1,800 · Repair quoted separately
Indicative ranges only. We provide written, itemised quotes before any work.
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