What a leak costs you for every month you leave it

What this calculator tells you

How much water a known rate of loss wastes over five periods, what that costs at your own rate, and how long the loss has to run before the water has cost what the repair costs.

• The cumulative volume at one week, one month, three months, six months and twelve months
• That volume in cubic metres and what it costs at your rate
• The break-even point against a repair quote, in days
• What that comparison justifies doing, which is sometimes nothing urgent

It reports no rate of loss, because it consumes one rather than producing it, and no severity, because a cost is not a classification. Four of the six standard attributes are absent here and that is what an honest scope looks like.

It also reports no damage cost, no insurance excess and no estimate of what a ruined floor is worth. None of those can be sourced for a particular property, and a number nobody can check would make every figure next to it less believable.

How to take the measurement

There is nothing to measure here. This calculator has no input of its own: it needs a rate of loss you have already measured, and a rate per cubic metre you can read off your bill.

• A rate of loss in litres per hour, measured rather than guessed. An overnight meter test with everything closed is the way to get one.
• Your volumetric rate per cubic metre, from your own bill or your company's charges scheme. If your bill covers sewerage on a share of metered volume, that share is part of the cost of a leak too.
• A repair quote, if you have one. Without it the table still works and the break-even does not.

The first of those is the one that has to be real, because everything on this page is a multiplication of it and an estimate multiplied by 8,760 hours is a very large estimate. measure your current rate of loss in litres per hour is how to get a measured one.

And the second decides the entire answer, since cost is the only output here and it is a straight function of the rate. your supplier rate per cubic metre explains where to find yours and why this site does not quote it for you.

Using the calculator

What your result means

The volume column is exact arithmetic. The cost column is that volume at the rate you gave. The useful part is usually neither of them on its own, but how the total compares with what you already use.

That comparison is the honest way to size a leak without quoting a price, because a percentage on your volume is a percentage on the part of your bill that moves with volume. No rate is needed to understand it and no rate can make it wrong.

It does overstate the effect on your bill, though, and the overstatement is worth knowing. A standing charge does not change with how much water you use, so a bill that goes up 9 per cent in volume goes up less than 9 per cent in total. The bigger the fixed part of your bill, the smaller the proportional effect of any leak on it.

Then the break-even. If you have a repair quote, the calculator divides it by what the leak costs per day and tells you how many days of leaking equal the price of fixing it. That is the only genuinely decision-shaped number on this page, because both halves of it are yours rather than ours.

Read the break-even in whichever direction it points, including the inconvenient one. If the water takes years to cost what the repair costs, then on water alone the repair does not pay for itself, and this page will say so rather than finding another argument. There may still be good reasons to fix it, and they are damage and not wasting water, but the bill is not one of them and pretending otherwise would be a sales pitch with a calculator attached.

How the calculation works

Two multiplications and one division, and nothing else is in here.

• Volume in litres = your rate × 24 × the number of days
• Volume in cubic metres = that ÷ 1,000
• Cost = cubic metres × your rate per cubic metre, plus the sewerage element where your bill charges one
• Break-even in days = the repair quote ÷ the cost of one day of leaking

The month is a twelfth of a year rather than 30 or 31 days, so three months, six months and twelve months add up exactly and nothing is lost to rounding between rows.

What this calculator assumes, and it is a bigger assumption than it looks

That the rate you measured carries on unchanged for the whole period. Every table of this kind assumes it and almost none of them say so.

This site has no source for how the rate of a household leak changes over time, so it is not asserted in either direction. What that means for you is that the table is a conditional rather than a prediction: this is what it costs IF it carries on as it is. A loss that is growing will overtake these figures. One that has partly sealed itself, which does happen, will not reach them.

The reason to name both directions rather than only the first is that only the first sells anything. A page funded by a leak detection company that quietly assumed every leak worsens would be putting a thumb on the scale in its sponsor's favour, using an assumption nobody could check. So the assumption is stated, and it is stated as an unknown.

The practical answer to the assumption is to measure again rather than to model it. Two meter tests a month apart tell you whether your leak is growing, and that is worth more than any assumption either of us could make about it.

Assumptions and sources

The arithmetic here needs no citation. Twenty-four hours in a day, a thousand litres in a cubic metre and a twelfth of a year in a month are definitions rather than findings, and they are listed above so you can see there is nothing else hiding in the calculation.

The one figure that is not a definition is the household comparison. It uses 136.5 litres per person per day, the Environment Agency figure for England in 2024 to 2025, scaled to four people. It is England only, it is a reference point rather than a target, and it differs from your own metered volume in three documented ways, set out in full on the consumption page.

• No supplier rate is quoted anywhere on this page or anywhere on this site, because not one has been verified. The cost column uses the rate you supply and nothing else.
• No damage cost appears, because it cannot be sourced for a particular property.
• No assumption is made about whether a leak worsens over time, because no source for that was found.

That last one is an absence rather than a caveat, and it is the largest uncertainty on the page. Everything else here is exact arithmetic on numbers you supplied. The only thing that can make the table wrong is the future, and neither of us knows what the leak does next.

What to do next

Four things, and the order is by what each one costs you.

• Check the rate you entered was measured rather than estimated. Everything here is that number multiplied by up to 8,760 hours, so an error in it is magnified by the same amount.
• Read your own volumetric rate off your bill, and check whether sewerage is charged on a share of your metered volume, because if it is then the water half is not the whole cost.
• Compare the twelve month figure against your own annual volume rather than against the four-person example. A leak that is 9 per cent of a large household is a different proposition from 9 per cent of a small one.
• Measure again in a month. That answers the one question this calculator cannot, which is whether the loss is steady, and it costs nothing but a second night with everything turned off.

If the break-even lands years away, that is a real answer and it is worth acting on: book the repair when it suits you rather than paying an emergency rate to save water that is not worth the premium. If it lands inside a few weeks, the arithmetic has made your decision for you.

Either way the figure only means what the rate behind it means. measure your current rate of loss in litres per hour again before acting on a number that came from a reading you took months ago.

Common questions