Why Is My Water Bill So High All of a Sudden?

First, rule out the boring explanations

Before you assume the worst, check whether Severn Trent has moved you from estimated to actual readings. If the last few bills were estimates and this one is a real reading, the jump may simply be catching up on months of under-billing. Compare the reading on the bill with the number on your meter, which for most Derby homes is in a small chamber in the pavement or driveway near the boundary, or under the kitchen sink in newer builds.

Then think about the billing period itself. A household of four typically uses around 350 to 450 litres a day. A visiting relative, a new washing machine, a paddling pool in July, or a garden sprinkler left on overnight can add thousands of litres in a single quarter without anyone noticing. If none of that applies and the increase is sudden and large, keep reading.

The overnight meter test

This is the single most useful check you can do, and it costs nothing. Last thing at night, make sure every tap is off, no appliances are running, and nobody will flush a toilet. Write down the full meter reading including the small red digits. First thing in the morning, before anyone uses any water, read it again.

If the numbers have moved, water is passing through the meter while nothing should be using it. A small leak might only shift the red dials by a litre or two, while a burst supply pipe can register 20 to 100 litres an hour. As a rough guide, a leak of 10 litres an hour adds around 88,000 litres a year, which on current Severn Trent metered rates is likely to add well over 200 pounds to your annual bill, and more if you are also charged for sewerage on that volume.

• Take a photo of the meter each time so you have a timestamped record
• Do not stop the stopcock during the test; you want to measure the whole system
• If your meter is shared or unreadable, ask Severn Trent to check it, which they do free of charge

Where the water usually goes

In our experience the culprits fall into a few groups. Toilets are the most common and the easiest to miss. A worn flush valve or float lets water trickle from the cistern into the pan continuously. It is often silent, but a sheet of toilet paper held against the back of the pan will show a damp line. A single leaking toilet can waste 200 to 400 litres a day.

Next are underground supply pipes. Many houses in Derby, Allestree, Mickleover and Chaddesden still have the original galvanised steel or early plastic supply pipes from the 1950s to 1970s, and they corrode or split at joints. The ground may look dry because the water drains into the subsoil. Inside the house, hot and cold pipes buried in concrete floors, especially in bungalows and ex-council properties, fail at the point where the pipe passes through the slab. A patch of floor that feels warm, a boiler that keeps losing pressure, or a damp skirting board with no obvious source are all classic signs.

• Toilet cistern overflow running into the pan
• Split or corroded supply pipe between the meter and the house
• Pipes under solid floors, often under a kitchen or hallway
• Outside taps and garden irrigation left slightly open
• Leaking pressure relief valve on an unvented hot water cylinder

Isolating the leak yourself

You can narrow it down further with the internal stopcock, which is usually under the kitchen sink. Close it fully and watch the meter for 15 minutes. If the meter stops, the leak is inside the house. If it keeps turning, the leak is on the supply pipe between the meter and the stopcock, which is your responsibility from the boundary inwards.

For an internal leak, turn off the valves to each toilet and the cold feed to the hot water cylinder one at a time and repeat the meter check. Older stopcocks can seize, so do not force one that has not been turned in years; a snapped stopcock creates a bigger problem than the one you started with.

When to call a leak detection specialist

If the meter is moving and you cannot find the source, it is usually cheaper to have it located properly than to start lifting floors on a guess. We use acoustic listening equipment, tracer gas and thermal imaging to pinpoint leaks under floors and along supply pipes to within a few centimetres, which means the repair is one small excavation rather than a trench across the garden or a whole floor up.

A domestic trace in the Derby area typically takes two to three hours. Costs depend on the size of the property and how much of the pipework is buried, but you should expect a fixed fee for the survey rather than an open-ended hourly charge, and a written report you can give to your insurer. Most home insurance policies in the UK cover trace and access, so the cost of finding the leak and making good afterwards is often claimable even when the pipe repair itself is not. It is also worth contacting Severn Trent once the leak is fixed; they will usually offer a leak allowance that reduces the bill for water lost to a leak you have now repaired.