Unexplained High Water Usage? Checks to Do Before You Call Anyone

A water bill that jumps with no obvious reason is worrying, partly because there is nothing to look at. No drip, no stain, no puddle. The good news is that most of the detective work can be done by you, in an evening, with a torch and a notebook. The checks below go from the quickest to the most involved, and by the end you should know whether water is being lost, whether it is inside or outside the house, and whether it is something you can fix yourself.

These checks assume you have a water meter. If you are not metered, your bill is not based on how much water you use, so a leak would not normally raise it, although it is still worth fixing.

Is the higher bill based on a real meter reading?

Before hunting for a leak, check the bill itself. Look for whether the reading was actual or estimated. An estimated bill followed by an actual reading can produce a large catch-up charge that looks like a spike in use but is really several months of normal use arriving at once.

• Find the meter and write down the full reading, with the date and time.
• Compare it with the reading printed on the bill.
• Compare the bill with the same period last year, not with the previous bill, because use changes with the seasons.
• Think about changes at home: more people living there, a new baby, working from home, a hot tub or paddling pool, garden watering in a dry spell, or a new appliance.

If the reading matches the bill and nothing at home has changed, move on to the meter test.

How do you test your water meter for a leak?

Meters are most often in a chamber under a small cover at the front boundary or in the pavement, though some are inside, near the internal stopcock. Many have a small star, wheel or flashing symbol that moves whenever water is flowing, which makes this test much quicker.

1. Stop every use of water. Turn off taps, the washing machine, dishwasher, any water softener and any garden irrigation. Do not flush toilets.
2. Let everything finish filling. Wait until toilet cisterns are quiet and any cold water tank in the loft has stopped refilling. This can take a while after a bath or shower.
3. Take a reading. Write down every digit, including the red or small figures, or photograph the dial. Note whether the flow indicator is moving.
4. Wait. Leave it for at least an hour without using water. The overnight version is more reliable: read the meter last thing at night and first thing in the morning before anyone uses water.
5. Read it again. Any movement means water has passed through the meter while nothing was supposed to be using it.

A tiny movement over a whole night can come from an appliance or a cistern topping up, so repeat the test before drawing a conclusion. A steady movement, or a flow indicator that keeps turning, is a clear sign that water is being lost.

Is the leak inside or outside the house?

If the meter moved, the next step splits the property in two using the internal stopcock. This works when the meter is at the boundary and the stopcock is where the supply pipe enters the building.

1. Close the internal stopcock fully, turning it clockwise. If it is stiff, do not force it.
2. Repeat the meter test.
3. If the meter still moves, water is escaping between the meter and the stopcock. That usually means the underground supply pipe, and our guide to underground supply pipe leaks explains what happens next.
4. If the meter stops, the loss is inside the house, on the pipework or a fitting after the stopcock.

Two things can confuse this test. An old stopcock may not close completely, which can make an internal leak look external. And if the meter is inside the house, a leak on the pipe before the meter will not show on it at all. If you are not sure the stopcock is shutting off fully, open a cold tap in the kitchen with the stopcock closed: the flow should stop within a few seconds.

How do you check a toilet for a silent leak?

Toilets are one of the most common causes of unexplained water use, because a faulty flush valve can let water trickle into the pan all day without making much noise. The dye test finds it.

1. Take the lid off the cistern once it has finished filling.
2. Add a few drops of food colouring to the water in the cistern.
3. Do not flush. Wait at least fifteen to thirty minutes.
4. Look in the pan. If coloured water has appeared, the flush valve or its seal is letting water through.
5. Flush afterwards to clear the colour, and repeat for every toilet in the house.

Also watch the water level in the cistern. If it rises above the overflow and trickles away, the fill valve is not shutting off properly. Depending on the cistern, that water goes into the pan or out through an overflow pipe to the outside wall. A faint trickling sound, or a thin line of water running down the back of the pan, are other giveaways. Replacing a flush valve washer or a fill valve is usually a small plumbing job.

What should you check in the loft?

If the house has a cold water storage tank, its float-operated valve should shut off once the tank is full. When the valve fails, the tank keeps filling and the excess goes out through the overflow pipe, which usually ends on an outside wall or over a gutter. Walk round the outside of the house and look for any pipe that is dripping or has left a stain or a green streak below it. A small feed and expansion tank for an older heating system works the same way and can overflow in the same manner.

In the loft itself, look for wet insulation, damp boards or a damp ceiling below the tank. Take care moving around the loft and only step on joists or boarded areas.

Could an outside tap or outbuilding be the cause?

Pipes outside the main house are easy to forget and are the ones most likely to be damaged by frost.

• Outside taps. Check for a dripping spout, a leak at the wall where the pipe comes through, or water running from a hose connector left on.
• Garages, sheds and garden rooms. Supplies to these are often run in plastic pipe through the garden and can be damaged by digging or frost.
• Irrigation and automatic top-ups. Timers can be set wrongly, and pond or water feature top-up valves can stick open.
• Wet patches. Look for an area of lawn that stays greener or softer than the rest, or a path that never quite dries.

Could an appliance or the hot water system be using the water?

• Water softeners regenerate automatically and can use more water than expected if they are set incorrectly or a valve sticks.
• Washing machines and dishwashers can have a faulty inlet valve that lets water through when the machine is off. Check the drain hose and the floor under the machine.
• Unvented hot water cylinders have a safety discharge that runs into a tundish, a small open funnel on the pipe near the cylinder. Water running through the tundish when nobody is using hot water is a sign of a fault and needs an installer qualified to work on unvented systems.
• Combi boilers can discharge water through the pressure relief pipe outside. That is heating system water, which is only replaced when someone tops the system up through the filling loop, so on its own it rarely explains a large rise on the meter.

What if every check comes back clear?

If the meter moves with everything off, the stopcock test says the leak is inside, and there is no dripping toilet, overflow, tap or appliance, the loss is probably on hidden pipework: under a floor, inside a wall or in a boxed-in section. That is where signs such as a musty smell, a warm or cold patch on the floor or a faint hiss behind a wall become useful. Our guide to the signs of a hidden water leak covers what to look for.

Keep your meter readings, with dates and times, in one place. They are useful to the engineer and to your water supplier, and they show whether the loss is steady or intermittent.

When should you call a leak detection specialist?

Call a specialist when your own checks confirm water is being lost but you cannot see where. A survey normally starts by repeating the meter and stopcock tests, then uses acoustic listening, thermal imaging, moisture readings or tracer gas depending on whether the loss is inside or outside. Our published prices start at £150 for acoustic or thermal surveys, and the combined detection package is £250 to £500. Call 020 3912 0200 with your meter readings to hand.

Frequently asked questions

Why is my water usage so high when I have no leak?

Often it is an estimated bill being corrected, a change in how many people are at home, garden watering, or a toilet that trickles silently. A meter test with everything turned off tells you whether water is really being lost.

How much can a leaking toilet waste?

It depends on the fault. A slow seep may barely register, while a fill valve that never shuts off can run continuously. The dye test and the meter test show whether yours is losing water, whatever the amount.

How do I know if the leak is on my side of the meter?

With the meter at the boundary, any movement while all water use is off means water is passing through the meter towards your property. Closing the internal stopcock then tells you whether it is being lost in the ground or inside the house.

Can I check for a leak if I do not have a water meter?

You cannot do a meter test, but you can still do the dye test, check overflows, outside taps and appliances, and listen at the stopcock with the house silent. A specialist can check the supply pipe using other methods.

Should I keep the stopcock closed until the leak is found?

If the tests show a leak inside the house and water is causing damage, closing the stopcock when you do not need water limits the loss. If the leak is on the underground supply pipe, closing the internal stopcock will not stop it.