How this calculator works
A leak wastes water continuously, so even a slow drip is measured in litres a day. The United States Geological Survey defines a drop at about 0.25 mL, based on 15,140 drips to a US gallon, so a tap dripping 30 times a minute loses 0.25 x 30 = 7.5 mL a minute, or 10.8 litres a day. Multiplying by the number of taps and the days gives the total. The water is metered at the same rate as water you use on purpose, and most municipalities also charge sewer rates on the volume, so the cost per cubic metre is the combined water and sewer price. If the tap is on the hot side, the water is heated and then poured down the drain, which wastes the energy as well: about 0.052 kWh to heat a litre from 15 to 60 degrees Celsius. A worn washer or cartridge is usually a cheap fix, and a single dripping tap can be worth a few thousand litres a year.
Formula
water per day (L) = faucets x drips per minute x 0.25 mL x 60 x 24 / 1000. water over the period = per day x days. annual water = per day x 365. bathtubs = annual water / 150 L. cost = annual water / 1000 x combined price per m3. If heated, energy (kWh) = annual water x 0.0522 and emissions = energy x 0.12 kg CO2e per kWh.
Worked example
One tap dripping 30 times a minute wastes 1 x 30 x 0.25 x 1,440 / 1,000 = 10.8 L a day, or 3,942 L a year. That is 26.3 bathtubs. At $2.50 per cubic metre the combined water and sewer charge is 3.942 x 2.50 = $9.86 a year. If the water is heated, the energy lost is 3,942 x 0.0522 = 205.8 kWh, emitting 24.7 kg CO2e on the national average grid.
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Frequently asked questions
Is a drip really that much water?
At 30 drips a minute, about 11 litres a day, which is more than a typical person drinks in a week. A faster drip or a small stream can reach hundreds of litres a day, and a leaking toilet flapper can waste far more.
Why does the drop size matter?
A smaller or larger drop changes the total proportionally. The 0.25 mL figure is a standard used by the USGS calculator and matches a typical faucet; a very slow drip forms smaller drops, so the volume per drip can be lower.
Does the sewer charge apply to leaked water?
In most Canadian municipalities, yes: the sewer charge is based on metered water use, and a leak goes through the meter even though it never reaches the sewer. Some utilities offer a leak adjustment, so ask before assuming the full charge stands.
How do I fix it?
A compression faucet usually needs a new washer; a cartridge or ceramic-disc faucet needs a new cartridge. Both are inexpensive. If the leak is at the spout and the tap is a quarter-turn type, the cartridge is the usual cause.
Sources
- United States Geological Survey, Water Science School: drip calculator and the volume of a water drop
- Environment and Climate Change Canada: emission factors and reference values for greenhouse gas quantification (national inventory edition, updated annually)
- Environment and Climate Change Canada: municipal water use and conservation