Drip Faucet Calculator

Background.

A dripping tap is the easiest plumbing problem to ignore and one of the easiest to quantify. Count the drips for fifteen seconds, multiply by four, and this calculator turns that number into gallons per day, per month and per year, plus what it costs at your own water and sewer rates.

The conversion rests on one figure: 15,140 drips per US gallon. That comes from the US Geological Survey, which is refreshingly blunt about it — there is no scientific definition of the volume of a faucet drip, so the USGS measured a number of kitchen and bathroom faucets and settled on a quarter of a millilitre per drip. Everything downstream of that assumption is exact arithmetic, but the assumption itself is a judgement, and the answer is an estimate rather than a measurement.

How much of a judgement? EPA WaterSense says a faucet dripping once per second can waste more than 3,000 gallons a year. The USGS quarter-millilitre drip gives 2,082.96 gallons for the same leak. The gap is 44 percent, and all of it is the assumed drip size — EPA's headline implies a drip of about 0.36 millilitres. This page reports the USGS arithmetic because the USGS publishes its assumption and can therefore be checked, and it names the EPA figure right beside the result rather than quietly picking a side.

The sewer rate is the part people forget. Most utilities bill sewer service on metered water volume, so every gallon that drips down the drain is charged twice — once as water in and once as sewage out. That is why there are two rate fields here. At five dollars for water and six for sewer per thousand gallons, a one-drip-per-second tap costs about $22.91 a year, which is less than a plumber's call-out and considerably more than a washer.

One drip per second sounds trivial and is not: it is 86,400 drips a day and 31,536,000 a year. Even a slow ten-drip-per-minute weep still loses 347.16 gallons annually. And a dripping tap is the visible member of a family — EPA puts household leaks at nearly a trillion gallons a year nationwide, with nine percent of homes losing 50 gallons a day or more, most of it from running toilets nobody can hear.

What is drip faucet calculator?

A drip faucet calculator converts a counted drip rate into a volume of water over time, and then into money at your own utility rates. The arithmetic is drips per minute times 1,440 minutes per day times the number of dripping fixtures, divided by 15,140 drips per gallon, then scaled to a 365 day year.

The one soft number in the chain is the drip volume. A drip is not a defined quantity: its size depends on the fitting, the water pressure and the surface tension at the spout. The USGS uses a quarter of a millilitre, having measured a number of household faucets, and that is the assumption this page implements and states.

This calculator estimates loss from a visible, countable drip. It does not detect leaks you cannot see. For those, shut every fixture in the house and watch the water meter for fifteen minutes — anything that moves is a leak, and a running toilet flapper typically wastes far more than any tap.

How to use this calculator.

1. 01Count the drips from the tap for fifteen seconds and multiply by four to get drips per minute. One drip per second is 60.
2. 02Enter how many fixtures are dripping at roughly that rate.
3. 03Enter your water rate per 1,000 gallons from your utility bill. If the bill is in hundreds of cubic feet, one CCF is 748 gallons.
4. 04Enter your sewer rate per 1,000 gallons as well — most utilities bill sewer on metered water, so a leak is charged twice. Enter 0 if you are on septic.
5. 05Read the annual waste and cost, and compare them against the price of a washer or cartridge.

The formula.

Drips per day is drips per minute multiplied by 1,440 minutes and by the number of dripping fixtures — for one tap at 60 drips per minute, that is 86,400 drips a day and 31,536,000 a year. Dividing by 15,140 drips per US gallon gives 5.7067371202 gallons a day, which over a 365 day year is 2082.9590488771 gallons, or 7884.857729209 litres using the exact 3.785411784 litres per gallon. The monthly figure is the year divided by twelve, giving 173.5799207398 gallons — a mean 30.42 day month, so it will not match a 28 or 31 day billing period exactly. Cost is the annual gallons divided by 1,000 and multiplied by the water and sewer rates combined: at $5 and $6 that is 2.0829590489 thousand-gallon units times $11, or $22.9125495376 a year and $1.9093791281 a month. The 15,140 constant comes from the USGS assumption of a quarter-millilitre drip; for comparison, EPA WaterSense's figure of more than 3,000 gallons a year for the same one-drip-per-second leak implies a drip of about 0.36 millilitres instead. All arithmetic is carried at full precision and rounded only at the final result.

A worked example.

Frequently asked questions.

References& sources.

1. [1]US Geological Survey, Water Science School — Drip Calculator: How Much Water Does a Leaking Faucet Waste? The USGS states there is no scientific definition of the volume of a faucet drip, adopts 1/4 mL after measuring a number of kitchen and bathroom faucets, and uses 15,140 drips per US gallon.
2. [2]US EPA WaterSense — Fix a Leak Week: a leaky faucet dripping at one drip per second can waste more than 3,000 gallons per year; household leaks waste nearly 1 trillion gallons annually nationwide; nine percent of homes have leaks wasting 50 gallons or more per day; the average household's leaks exceed 9,300 gallons a year.
3. [3]NIST Special Publication 811 (2008), Guide for the Use of the International System of Units (SI) — the US gallon as exactly 3.785 411 784 litres, used for the litres output and for the drip-volume comparison.