Hong Life CalculatorsUnderstanding the leaky tap and toilet water waste calculator — concept and principle
A dripping tap or a toilet that keeps running looks harmless, but it wastes water every minute of every day. This calculator estimates how many litres a leak wastes in a year and what it costs at your water price, so you can decide how urgently to fix it.
How it is calculated
- Tap litres per year = drips per minute × mL per drip × 60 × 24 × 365 ÷ 1,000
- Toilet litres per year = running toilet (L/h) × 24 × 365
- Litres per year = tap litres + toilet litres
- Cost per year = litres per year ÷ 1,000 × water price per m³
Count drips for one minute. A typical drip is about 0.25 mL, but drip size varies with the tap and pressure; you can check yours by collecting drips in a measuring jug. Enter 0 for the toilet if it does not run.
The principle
A leak is a small, constant flow, and constant flows add up because a year has 525,600 minutes. One drip per second is 60 drips a minute; at 0.25 mL each that is 15 mL a minute, 21.6 L a day and about 7,900 L a year. A running toilet can be far worse because water flows through the overflow or past a worn flapper continuously. Dividing litres by 1,000 converts to cubic metres, the unit most water bills use.
Worked example
- Inputs: 60 drips per minute, 0.25 mL per drip, toilet 0 L/h, water $3 per m³.
- Per minute: 60 × 0.25 = 15 mL.
- Per year: 15 × 60 × 24 × 365 ÷ 1,000 = 7,884 L.
- Cost: 7,884 ÷ 1,000 × $3 = $23.65 per year.
| Drips per minute | Litres per year |
|---|---|
| 15 | 1,971 |
| 30 | 3,942 |
| 45 | 5,913 |
| 60 | 7,884 |
| 75 | 9,855 |
| 90 | 11,826 |
| 120 | 15,768 |
How to read the result
The cost of a dripping tap is modest, but the water volume is significant, and fixing a washer or cartridge is usually cheap. If your water is heated, a dripping hot tap also wastes the energy used to heat it. Leaks you cannot see matter more: a meter that keeps moving when no water is being used points to a hidden leak.
Common mistakes
- Guessing the drip rate instead of counting for a full minute.
- Leaving out sewer charges when they are billed on water used.
- Ignoring a quietly running toilet because it makes no noise.
Frequently asked questions
How can I check if my toilet is leaking?
Add a few drops of food colouring to the cistern, wait without flushing, and see if colour appears in the bowl.
How do I find a hidden leak?
Turn off all taps and appliances, read the water meter, wait an hour or two, and read again.
Does a leaking hot tap cost more?
Yes, add the cost of heating that water, which you can estimate with the shower cost calculator.
Sources: U.S. Geological Survey, Water Science School — drip calculator · U.S. EPA WaterSense — Fix a Leak Week