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· 4 min read
How to Work Out What a Leak Is Costing You
Heshan Fernando
Co-founder & COO
A dripping tap is annoying and cheap. A running toilet is silent and expensive. Most people worry about the first and never notice the second, which is exactly the wrong way round.
Putting numbers on both changes which one you fix first.
The arithmetic
A drip is roughly a quarter of a millilitre. That sounds like nothing, and at one drip per second it is nothing — until you multiply by 86,400 seconds in a day.
litres per day = drips per minute × 0.25 ml × 1440 ÷ 1000
At 60 drips a minute, that’s around 15 litres a day, or over 5,000 litres a year. At a typical water rate that’s a modest annual cost — enough to justify a washer, not enough to panic about.
A running toilet is a different scale entirely. A continuously running fill valve or a leaking flush valve can pass hundreds of litres a day. It’s often silent, or quiet enough to be mistaken for normal plumbing noise, and it can run for months before anyone notices — usually when the bill arrives.
The other cost people forget: if the leak is on the hot side, you’re also paying to heat water that’s going down the drain.
Why people get stuck here
- Silent leaks. The expensive ones don’t announce themselves.
- Unmetered supply. With no meter there’s no feedback, so a leak costs the household nothing directly and gets ignored.
- Wastewater charges. Many bills charge for wastewater based on water supplied, so a leak can be charged twice.
- Underground leaks. A supply pipe leaking between the meter and the house is the homeowner’s responsibility in many places, and it’s invisible.
How to find a leak you can’t see
The meter test
Turn off every water-using appliance and don’t use anything for two hours. Read the meter at the start and end. Any movement means water is going somewhere.
The toilet dye test
Put a few drops of food colouring in the cistern and don’t flush. If colour appears in the bowl within fifteen minutes, the flush valve is leaking.
Listen at night
A quiet house makes a running toilet or a hissing valve audible when it isn’t during the day.
| Leak | Typical Loss | Notice It? |
|---|---|---|
| Dripping tap | ~15 L/day | Yes — irritating |
| Steady trickle | 100+ L/day | Sometimes |
| Running toilet | 200–700 L/day | Often not |
| Underground supply pipe | Very high | No — meter test only |
Common mistakes to avoid
- Fixing the visible drip and ignoring the silent toilet.
- Assuming a high bill is a pricing change rather than checking the meter.
- Ignoring a damp patch on a wall or a warm spot on a floor, both classic signs of a hidden leak.
- Forgetting the hot-water case, where you pay twice — for the water and the energy.
- Not knowing where your stopcock is before you need it.
How to do it with Leak Loss Calculator
The Leak Loss Calculator converts a drip rate or flow into daily, monthly and annual loss and cost.
- Identify the leak type — a running toilet is in a different league from a tap.
- Count drips over a minute, or time how long a container takes to fill.
- Enter your water rate, and remember wastewater is often charged on top.
- Compare the annual figure against the cost of the repair.
Waterwise and most water companies publish leak-finding guides and sometimes free repair schemes. Other household calculators are in the tools directory.
Frequently asked questions
Which leak wastes the most?
A continuously running toilet, by a wide margin — it can waste hundreds of litres a day and dwarf every dripping tap in the house. It’s also the easiest one to miss.
How do I find a leak I can’t see?
Read the meter, use no water for two hours, and read it again. Any movement means something is leaking somewhere between the meter and your taps.
Is a dripping tap worth fixing?
Financially it’s usually a small sum, but a washer costs less than the water, and on a hot tap you’re paying for the heating too.
Final thought
Do the meter test once a year. It takes two hours of not using water and it’s the only way to find the leaks that cost real money.