A sudden jump in your water bill usually comes down to one of three things: a hidden leak, a running toilet, or a dripping tap. The quickest way to tell is the meter test: turn off all water, wait 30 minutes, and see if the meter still moves. If it does, water is escaping somewhere and it is worth investigating.
A water bill that doubles overnight is alarming, especially when nothing in the house has changed. The good news is that most causes are findable, and some are a five-minute fix. Here is how to work through it, starting with the test that rules a leak in or out.
Start with the two-minute meter test
Before you blame the tariff, check for water leaving the house when it should not be:
- Turn off every tap and any water-using appliance (dishwasher, washing machine).
- Find your water meter (usually near the boundary, by the pavement, or under the kitchen sink) and note the reading.
- Wait about 30 minutes without using any water at all.
- Read the meter again.
If the reading has moved with everything switched off, water is escaping somewhere. That is the clearest single sign of a leak or a running toilet, and it tells you the high bill is not just a price rise.
The usual suspects
If the meter moves, or even if it does not but the bill still looks wrong, run through these:
- A running or leaking toilet. The most common culprit. A worn flush valve lets water trickle from the cistern into the bowl, quietly and constantly. Water companies estimate this can waste hundreds of litres a day.
- Dripping taps. A steady drip looks harmless but adds up. UK water companies put a single dripping tap at several thousand litres a year.
- Outdoor taps and hoses. A garden tap left slightly on, or a leaking hose connector, can run for weeks unseen.
- More water use than usual. A new baby, a returning student, a hot Cornish summer of garden watering and paddling pools all show up on a meter.
- A price or tariff change. Worth checking, but it rarely doubles a bill on its own.
- An estimated or misread meter. If the bill is based on an estimate, submit an actual reading and ask for it to be corrected.
When it points to a hidden leak
If the easy causes are ruled out and the meter still creeps, the water is most likely going into the ground or under your floors. Watch for these alongside the high bill:
- A patch of floor that is warm, damp or never quite dries.
- The faint sound of running water when the house is silent.
- A drop in water pressure, or mould and a musty smell in one area.
- An unusually green or boggy patch on the lawn or drive above a buried pipe.
Our water leak guide goes through these warning signs in more detail. A hidden leak on the underground supply pipe between the meter and the house is a common one in Cornwall, and it will not fix itself.
What to do next
Fix the simple things first: a new flush valve or tap washer is cheap and can stop the bleeding straight away. If the meter test points to something hidden, that is the moment for a professional survey. We pinpoint the leak with non-invasive equipment, so you are not digging up a whole floor or drive on guesswork. See how our water leak detection service works, or our underground water leak detection if the leak is outside.
One more thing worth knowing if you are metered: South West Water runs a leak allowance that can credit your bill for the water lost through a qualifying leak once it is repaired. We explain how it works in our guide to the South West Water leak allowance.
Frequently asked questions
How do I know if a leak is causing my high water bill?
Turn off every tap and water-using appliance, then read your water meter. Wait 30 minutes without using any water and read it again. If the numbers have moved, water is escaping somewhere, which usually points to a leak or a running toilet.
Can a running toilet really raise my bill that much?
Yes. UK water companies estimate a constantly running toilet can waste hundreds of litres a day. Because it runs quietly, it can go unnoticed for months, which is why it is one of the most common reasons a metered bill climbs.
I am a South West Water customer. Can I get money back for a leak?
Possibly. South West Water offers a leak allowance for metered customers that credits your bill for water lost through a qualifying leak, once it is repaired. Eligibility and time limits apply, so check the current terms on the South West Water website.
My bill is high but the meter does not move. What now?
That usually rules out a live leak. Look instead at higher usage, a tariff change, or an estimated reading. Submit an actual meter reading and compare it with the bill before assuming the worst.
High bill and a meter that keeps moving?
We find hidden water leaks across Cornwall with non-invasive kit, then give you a clear written report. Fast response, no need to dig on guesswork.