A water bill that jumps for no obvious reason is one of the clearest signs of a hidden leak. These leaks are often out of sight, in a wall cavity, under a floor, or below ground. Because of that, you can be losing water for weeks before it shows up anywhere visible.
The good news is that most causes are checkable in an hour, without any specialist equipment. Therefore, work through the list below before assuming it needs a full leak detection survey.
Start with your water meter
If you have a water meter, this is the fastest way to check for a leak.
- Make sure no taps, appliances, or outside hoses are running anywhere in the house.
- Note the meter reading, then leave everything untouched for two hours.
- Check the reading again. If it’s moved, and nothing used water in that time, you have a leak somewhere on your side of the meter.
This test won’t tell you where the leak is. However, it confirms one exists before you start checking individual fixtures.
The usual suspects
Once you know there’s a leak, work through these in order. They’re the most common causes by far.
A running or leaking toilet — Add a few drops of food colouring to the cistern and wait fifteen minutes without flushing. If colour appears in the bowl, water is passing through the flush valve continuously. Nothing will look wrong from the outside.
A dripping tap or shower — A slow drip can seem trivial, but it runs constantly, every hour of every day. Over a full billing period, that adds up to far more than a single glance suggests.
An outside tap or hose connection — These sit outside and are easy to forget about, especially if a hose has been left connected over winter. A worn washer here can leak for months without anyone noticing.
A hidden pipe leak — If you’ve ruled out the fixtures above and the meter test still shows water loss, the leak is most likely in a pipe run you can’t see. That’s when it’s worth calling in professional leak detection, rather than guessing further.
When to call a plumber
Get in touch if the meter test confirms a leak but you can’t find an obvious cause. We use acoustic and thermal detection to trace a hidden leak, without needing to dig up a garden or lift a floor speculatively. Finding it accurately first is what keeps the repair itself small.
Frequently asked questions
How much can a hidden leak add to a water bill? It depends entirely on the size of the leak and how long it’s been running. There’s no single figure that applies to every case. Even a small, constant drip can add up to a noticeable jump over a full billing period. That’s because it runs every hour of every day, not only when a tap is in use.
Can a running toilet really cause a big bill increase? Yes, a worn flush valve is a common cause. It can let water run continuously into the pan without ever overflowing, so you might not notice it by eye at all. It’s also one of the easiest and cheapest things to check first, before assuming the problem is more complicated.
Do water companies help if a leak caused a high bill? Many do have a leak allowance policy, though the details vary between suppliers. Once you’ve had a leak found and fixed, contact your water company directly to ask, since they may adjust the affected billing period. Keep any invoice or report from the plumber who traced the leak, as most suppliers will ask for evidence.
Our leak detection page covers how we trace a hidden leak without unnecessary digging, from the acoustic equipment we use through to how we confirm a fix has worked. We cover this across leak detection in Gosport, Lymington plumbing emergencies and Portsmouth call-outs, as well as Southampton itself. If you’re weighing up the cost before getting someone out, our call-out cost guide explains what to expect. If you’re a landlord dealing with this in a rented property, our landlord’s guide to emergency plumbing covers who’s responsible for sorting it.