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Why Is My Water Bill So High?
Reviewed by the Devon Leak Detection team · Last updated June 2026
The short answer
A water bill that has jumped usually comes down to one of four things: a hidden leak, a silently running toilet, a genuine change in how much you use, or a billing or meter issue. The quickest test is to turn everything off and watch your meter. If it keeps ticking, water is escaping somewhere.
Opening a water bill that is far bigger than usual is unsettling, especially when nothing about your daily routine seems to have changed. The good news is that there is almost always a clear reason behind it, and many of the causes are things you can check yourself in an afternoon. This guide walks through the most common reasons a bill climbs, the simple tests that point to the culprit, and what to do if you live in Devon and think a leak is to blame.
The four usual suspects
When a metered bill rises sharply, it is rarely a mystery for long. Most cases trace back to a hidden leak, a toilet quietly losing water, a real change in your usage, or something on the billing side. Working through them in order saves money and stress.
1. A hidden leak
This is the cause people worry about most, and for good reason. A leak on the pipe that brings water into your home can run day and night without ever showing on the surface. Underground supply pipes, joints under floors, and connections behind walls can all weep slowly for weeks. Because the water often soaks away into the ground or drains quietly, you may never see a puddle, yet the meter keeps counting every litre.
A central heating system that keeps needing topping up, a water softener stuck in a regeneration cycle, or an outside tap with a worn washer can all add to consumption too. If your bill has crept up with no obvious explanation, a hidden leak is the first thing worth ruling out.
2. A running or leaking toilet
A toilet that does not seal properly is one of the most common and most overlooked drains on a water bill. When the flush valve or fill valve fails to seat, water trickles continuously from the cistern into the bowl. It often makes little or no sound, so it can go unnoticed for months. A single leaking loo can waste a surprising amount of water, often quoted in the region of 200 to 400 litres a day, which on a meter quietly adds up.
There is a simple way to check, covered in the DIY section below. If you have more than one toilet, test each one, because the leak might be in the bathroom you rarely use.
3. A genuine change in usage
Sometimes the bill is right and your habits have shifted without you really clocking it. More people living at home, a new baby with endless washing, longer showers, a hot spell with the garden hose out, a paddling pool, or filling a hot tub all push consumption up. Water use tends to rise in spring and summer for exactly these reasons. New appliances such as a power shower or an American-style fridge with a water line can also nudge the figure higher.
4. A meter or billing issue
Not every high bill means water is being lost. If a previous bill was based on an estimated reading rather than an actual one, you may have been undercharged for a while. When a real reading is finally taken, the bill catches up all at once and looks like a spike, even though your usage was steady. Check your bill to see whether it is marked estimated or actual.
Meters very rarely over-read, but it is not impossible. Your water meter belongs to South West Water and is theirs to maintain, so if you have worked through everything else and the numbers still do not add up, you can ask them about a meter accuracy check. Water charges also rise from time to time, so it is worth confirming whether part of the increase is simply a tariff change.
DIY checks you can do today
Before you call anyone, a few minutes of detective work can tell you a great deal. These checks are safe, free, and often pinpoint the problem.
The meter and stop-tap test
This is the single most useful test for spotting a hidden leak. Here is how to do it:
- Turn off every tap and appliance that uses water, and ask the household not to flush or run anything.
- Find your water meter (often near the boundary, in the pavement, or under the kitchen sink) and write down the exact reading, including the small dials.
- Wait an hour or two without using any water at all, then read the meter again.
- If the reading has moved when nothing was running, water is escaping somewhere on your side of the meter.
- To narrow it down, turn off your internal stop-tap (usually under the kitchen sink) and repeat. If the meter stops, the leak is inside the house. If it keeps moving, it is likely on the underground supply pipe between the meter and your home.
The toilet dye test
To catch a silently leaking loo, take the lid off the cistern and add a few drops of food colouring, or drop in a coloured tablet. Do not flush. Wait around 15 to 30 minutes, then look in the bowl. If colour has seeped through into the bowl without flushing, the cistern is leaking and water is being lost. A worn flush valve or fill valve is usually a low-cost fix for a plumber.
A quick walk round
Check under sinks and around the boiler for damp patches, listen for hissing near pipes, look for an unusually green or soft patch on the lawn or driveway, and keep an eye out for a drop in water pressure. Any of these can point to where water is going. Our guide to the signs of a water leak covers what else to look and listen for.
Who is responsible for the pipe?
Knowing where responsibility sits helps you decide what to do next. As a rough guide, the underground supply pipe that runs from the boundary of your property up to the first stop-tap inside your home is normally the homeowner’s responsibility to maintain and repair. The mains in the road and, in many cases, the external stop-tap at the boundary are the water company’s. The meter itself belongs to South West Water. If the leak is on your supply pipe, fixing it falls to you, but you may not have to swallow the cost of the wasted water, as the next section explains.
South West Water customers: reporting and leak allowance
If you are supplied by South West Water and you think a leak is behind your bill, you can report it to them directly, usually through their website. If the leak is on your private supply pipe and you are on a meter, South West Water may offer a leak allowance that credits your bill for some of the water lost once the leak has been repaired. Allowances are not automatic and the terms vary, so it is worth reading their current policy and keeping meter readings from before and after the repair to support a claim. As a general rule, leaks inside the home are less likely to qualify than leaks on the underground supply pipe, but it is always best to check directly with South West Water rather than assume. Our article on what to do if South West Water says you have a leak walks through the process step by step.
When to bring in a professional
If the meter test shows water moving with everything off, but you cannot see where it is going, that usually means the leak is underground or hidden behind a wall or floor. Digging up a driveway or lifting floors to go looking is expensive and disruptive. This is where professional leak detection earns its keep. Using non-invasive methods such as acoustic listening equipment, thermal imaging and tracer gas, a specialist can pinpoint the exact spot before anything is opened up, so any repair is targeted rather than guesswork. If you are in Devon and want it found quickly and cleanly, our water leak detection service covers the whole county. You can read more about how we work and the areas we cover on our Devon page.
A high bill is frustrating, but it is also a useful early warning. Catching a leak sooner rather than later keeps the water in your pipes, the damp out of your home, and the cost down on your next statement.
Frequently Asked Questions
Turn off every water-using tap and appliance, note your meter reading, then wait an hour or two without using any water and read it again. If the meter has moved when nothing was running, water is escaping somewhere on your side of the supply. That is the clearest sign of a hidden leak and a good reason to investigate further.
A toilet that does not seal properly can waste a lot of water silently, often quoted at around 200 to 400 litres a day. Because it usually makes little noise, it can run for months unnoticed. The food-colouring test (dye in the cistern, no flush, check the bowl) is a quick way to confirm whether yours is leaking.
If you are a metered customer and the leak is on your private supply pipe, South West Water may offer a leak allowance that credits your bill for some of the lost water once it is repaired. Allowances are not guaranteed and the terms vary, so check their current policy and keep meter readings from before and after the repair.
As a general guide, the underground supply pipe from your boundary to the first stop-tap inside your home is the homeowner’s responsibility, while the mains in the road and the meter belong to the water company. If you are unsure where the boundary sits, it is best to confirm directly with South West Water before arranging any repair.
If your habits are the same, look at whether your last bill was an estimated reading rather than an actual one, as an undercharge can catch up in a single spike. It is also worth checking for a hidden leak or a silently running toilet, and confirming whether water charges have simply risen since your last statement.
If the meter test shows water moving with everything off but you cannot see where it is going, the leak is probably underground or behind a wall or floor. A specialist can pinpoint it with acoustic equipment, thermal imaging and tracer gas, so the repair is targeted rather than guesswork. That saves digging up more than you need to.
Worried About a Leak in Devon?
If your meter keeps ticking with everything off, we can find the leak quickly and cleanly, before anything gets dug up. Get in touch for a free quote.