A drip faucet calculator answers a question that sounds trivial and is not: what does a drip actually cost? A single drop is about a quarter of a millilitre, which is nothing. The same drop repeated twenty times a minute, every minute, for a year is a few thousand litres, which is not nothing — and if it is coming out of the hot side, the energy that heated it costs more than the water itself.
Arb Digital publishes a free tools library built on transparent arithmetic, and this page is the small-scale counterpart to the water usage calculator. That tool totals what a household deliberately consumes across showers, laundry and irrigation; this one models a single unintended flow rate and prices it. They answer different questions and should not be used interchangeably: a leak does not appear in a fixture-by-fixture consumption model at all, which is exactly why leaks go unnoticed on a bill.
What This Drip Faucet Calculator Does
It turns a counted drip rate into a volume per day and per year, multiplies by the number of leaking fixtures, and then splits that volume into cold and heated portions. The cold portion costs only the water and sewer charge. The heated portion also costs the energy needed to raise that water through your temperature rise, adjusted for heater efficiency, plus the emissions of producing that energy.
The headline is the annual volume in litres with the gallon figure alongside. The four supporting boxes give the daily gallon rate, the annual water and sewer cost, the annual heating cost and the annual carbon dioxide equivalent from the heating. The bars underneath compare the two costs directly, which is the comparison most people get wrong before they run the numbers.
How to Use It
- Count drips for a full minute. Not ten seconds multiplied by six. Drip rates are irregular, and a short sample taken during a fast burst can double your answer.
- Check the drip volume. The default of a quarter of a millilitre is a standard assumption. To measure yours, catch the drips in a measuring container for ten minutes and divide.
- Set the hot-water share honestly. A dripping cold tap costs water only. A mixer left in the middle is drawing from both sides, and a leaking hot valve is entirely hot.
- Use your combined water and sewer rate. Most utilities bill wastewater volume from the metered water volume, so using the water rate alone typically halves the true cost of the leak.
- Enter the temperature rise, not the setting. If mains water arrives at 55°F and the heater is set to 125°F, the rise is 70°F. In winter the incoming temperature falls, so the same leak costs more energy.
The Formula / How It's Calculated
The chain is short and every step is exact arithmetic:
Litres per day = drips per minute × ml per drip × 1,440 ÷ 1,000 × fixtures. Annual litres = daily × 365, and gallons are litres ÷ 3.785411784. Heated gallons = annual gallons × hot share. Heat energy in BTU = heated gallons × 8.3454 lb per gallon × temperature rise in °F, since one BTU raises one pound of water by one degree Fahrenheit. That divided by 3,412.142 gives kWh, and dividing again by heater efficiency gives the energy actually bought.
Worked example with the values the page loads with. Twenty drips a minute at 0.25 ml is 5 ml a minute, which is 7,200 ml — 7.2 litres a day, or 2,628 litres a year. In gallons that is 1.90 a day and 694.3 a year. At 12.00 per 1,000 gallons the water and sewer cost is 8.33. Forty per cent of the volume is heated, so 277.7 gallons × 8.3454 lb × 70°F = 162,218 BTU, which is 47.5 kWh, or 52.8 kWh after dividing by 0.9 efficiency. At 0.16 per kWh that is 8.45 in energy, and at 0.40 kg CO2e per kWh it is 21.1 kg CO2e a year.
Note what that example shows: the energy cost slightly exceeds the water cost, from a leak that is only 40% hot. On a fully hot leak the energy is more than twice the water charge.
How Big Is This Compared With Everything Else in the House?
The default leak wastes 694 gallons a year. The US Environmental Protection Agency's WaterSense programme reports in How We Use Water that the average American family uses more than 300 gallons a day at home, roughly 70% of it indoors. Against that baseline a single slow drip is under a day's household use across a whole year — genuinely small.
That is not the whole picture, though, and the reason is scale and duration rather than rate. The EPA's Fix a Leak Week materials state that household leaks can waste nearly one trillion gallons of water annually nationwide, that the average household's leaks can account for more than 9,300 gallons a year, and that nine per cent of homes have leaks wasting 50 gallons or more per day. That last category is not a dripping tap at all — 50 gallons a day is a running toilet flapper or a failed valve, which is roughly 26 times the default leak here.
The practical reading: a drip is worth fixing because it is cheap to fix and because it is often the visible symptom of a fixture that is about to fail properly. It is not, by itself, a major line on a water bill. If your bill has jumped, look for a continuous flow rather than a drip, and use the water usage calculator to work out what your consumption should be so you can size the gap.
Why the Energy Cost Usually Beats the Water Cost
Water is one of the cheapest things a household buys per litre. Heating it is not. Raising a gallon of water by 70°F takes about 0.17 kWh at the meter once heater losses are counted, and in most markets that energy costs several times what the gallon of water itself costs.
The corollary is that the same drip has wildly different costs depending on which side of the mixer it comes from. Two identical taps, one cold and one hot, produce the same litre count and very different bills. This is the single most useful thing the tool tells you, and it is why the hot-water share is a required input rather than an assumption.
Efficiency matters more than people expect too. A 0.9-efficiency electric resistance heater and a 0.6-efficiency older gas unit differ by 50% in energy purchased for the same delivered heat. A heat pump water heater with an efficiency above 1 — because it moves heat rather than making it — will show a much smaller figure, and the input accepts values up to 1 only, so model those cases by adjusting the price per kWh instead. The electricity bill calculator is the better tool for whole-home energy pricing.
Where the Emissions Factor Comes From
The carbon figure is deliberately an input rather than a constant, because the same kilowatt-hour carries wildly different emissions depending on the grid supplying it and the year in question. The UK greenhouse gas reporting conversion factors 2025, published by the Department for Energy Security and Net Zero on 10 June 2025, provide annually revised factors for grid electricity and for natural gas, with a methodology paper explaining how each is derived. Other countries publish equivalent sets, and US regional figures come from the EPA's eGRID database.
Two details matter when you pick one. First, whether the factor is combustion-only or includes the well-to-tank emissions of producing and distributing the fuel — mixing the two bases in one analysis is a common error. Second, the year: grid factors change substantially as generation mixes shift, and a five-year-old factor can be badly out of date. Record both alongside any number you report.
If the water is heated by gas rather than electricity, use the gas factor and remember that the efficiency input is doing more work: a gas heater's standing losses are typically larger than an electric one's, so its effective efficiency across a year is lower than its rated figure.
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Browse Free Tools Talk to Arb DigitalCommon Mistakes to Avoid
- Sampling the drip rate for ten seconds — drips are irregular, and a short sample taken during a burst can double the annual figure.
- Using the water rate without the sewer rate — most utilities bill wastewater on metered volume, so leaving it out typically understates the cost by around half.
- Entering the hot water setting as the temperature rise — the rise is the setting minus the incoming mains temperature, and it changes with the season.
- Assuming a drip explains a large bill increase — a drip is a few hundred gallons a year. A continuously running toilet is tens of gallons a day, which is a different order of problem.
- Treating a carbon factor as permanent — grid intensity is revised annually, so any emissions figure needs its source and its data year attached.
Related Free Tools From Arb Digital
The water usage calculator models deliberate household consumption rather than leaks, the electricity bill calculator prices whole-home energy, and the litres to gallons converter and volume converter handle unit changes. For other footprints see the flight carbon footprint calculator, and use the percentage calculator for the supporting arithmetic. Everything else is in the free online tools hub.
Frequently Asked Questions
At twenty drips a minute and a quarter of a millilitre per drip, about 7.2 litres a day, which is roughly 2,628 litres or 694 US gallons a year. Both the drip rate and the drip volume are inputs here because both vary substantially between fixtures.
Because heating water usually costs more than the water itself. A dripping cold tap costs only the water and sewer charge, while the same drip on the hot side adds the energy to raise it through your temperature rise, adjusted for heater efficiency.
It is the assumption used in the widely cited USGS drip calculation and a reasonable default. Real drip size depends on the fixture and the aerator, so if the number matters, catch the drips in a measuring container for ten minutes and divide to get your own figure.
Yes, in almost every case. Most utilities calculate wastewater volume from metered water volume, so water that leaks away is billed twice. Using the water rate alone typically understates the cost of a leak by about half.
Rarely. A drip is a few hundred gallons a year. The EPA reports that nine per cent of homes have leaks wasting 50 gallons or more per day, which is a running toilet or a failed valve rather than a tap, and that is the kind of fault a large bill increase usually points to.
The difference between the temperature of the water arriving from the mains and your hot water setting, not the setting on its own. Incoming temperature falls in winter, so the same leak costs more energy in cold months than in warm ones.
The efficiency field accepts values up to 1, because it represents the fraction of purchased energy that reaches the water. A heat pump moves heat rather than generating it, so model it by dividing your price per kWh by its coefficient of performance instead of entering an efficiency above 1.
This tool performs arithmetic on figures you supply. It is not plumbing, energy or financial advice, and the costs it reports depend entirely on the rates, efficiency and emissions factor you enter.
