Last updated: October 2026
Two meters, not one
A water bill has a volume component (price per cubic metre or per 1,000 gallons), usually a fixed standing charge, and in many places a sewer charge calculated on the same volume. Hot water adds a second, larger cost that does not appear on the water bill at all: the gas or electricity used to raise its temperature.
The physics is unusually simple, which is why the arithmetic below is worth doing once. Heating water takes about 4.19 kilojoules per kilogram per degree, so one litre raised by one degree needs roughly 1.16 watt-hours.
What one shower costs
Take an 8-minute shower at 9 litres per minute — a standard head at normal pressure:
- Volume: 8 × 9 = 72 litres, or 0.072 m³.
- Water: at $3.00 per m³, about $0.22.
- Heating: from 15 °C mains water to 40 °C is a 25-degree rise: 72 × 4.19 × 25 = 7,535 kJ = 2.1 kWh, about $0.31 at $0.15 per kWh.
- Total: about $0.53, and roughly 60% of it is heat.
A full bath is worse on both counts: 150 litres is about $0.45 of water plus 4.4 kWh, around $1.10 all in. That is why switching one bath a week to a shower is a bigger saving than most people expect.
The whole house, for a family of four
| Use | Per year | Notes |
|---|---|---|
| Showers (4 people, daily, 8 min) | ≈ 105 m³ | plus about 3,050 kWh of heating |
| Toilets (5 flushes each per day, 9 L) | ≈ 66 m³ | no heating, but sewer charges apply |
| Laundry (4 cycles a week, 50 L) | ≈ 10 m³ | older machines use twice this |
| Kitchen, cleaning, drinking | ≈ 12 m³ | dishwasher 10–15 L per full load |
| Total indoors | ≈ 193 m³ | water ≈ $580, plus ≈ $460 of water heating |
| Garden (summer only, 20 min a week) | ≈ 15 m³ | a hose moves 15–20 L per minute |
The pattern to notice: showers are roughly a third of the volume but nearly all of the heating bill, while toilets are a third of the volume and none of it. Any change that touches hot water saves twice — once at the meter and once at the boiler.
Where the cheap wins are
- Fix the running toilet first. A silently leaking flapper passes 200–500 litres a day — up to 180 m³ a year, comparable to every shower in the house. Put food dye in the tank, wait twenty minutes, and look at the bowl.
- Low-flow head. Going from 9 to 6 litres per minute cuts a shower to 48 litres and 1.4 kWh: about $0.35 per shower instead of $0.53. Four daily showers is roughly $260 a year, and the head costs less than one month of that.
- Shorter, not colder. Cutting two minutes off saves 18 litres and 0.5 kWh — the same as turning the temperature down by about 7 degrees, but nobody notices.
- Full loads only. Two half-loads use almost exactly twice the water and energy of one full load.
- Insulate the hot pipe run if the boiler is far from the shower: you are otherwise paying to heat the pipe before the water arrives.
What not to bother with
Replacing a working toilet to save two litres a flush rarely pays back inside a decade. Catching shower warm-up water in a bucket is a nice habit with a tiny effect — a few litres a day against a 72-litre shower. And if you are on a fixed standing charge with unmetered water, the volume side of this article does not apply to you at all; only the heating half does.
Run your own numbers
Our shower water calculator takes your shower duration and flow rate and returns litres, annual volume and cost; the appliance energy cost calculator handles the heating side for any appliance, and the hydration calculator covers the drinking-water half of the same topic. More long-form write-ups are listed on the guides index.
Frequently asked questions
How much does one shower cost?
At 9 litres per minute for 8 minutes that is 72 litres. Water at $3 per cubic metre costs about 22 cents, and heating those litres from 15 to 40 °C takes roughly 2.1 kWh, about 31 cents at 15 cents per kWh. So the shower costs about 53 cents, of which the majority is energy, not water.
What uses the most water in a house?
For a family of four, showers and baths usually lead at roughly 100–120 cubic metres a year, followed by toilets at 50–65, laundry at 15–20 and kitchen use at 10–15. Outdoor watering can overtake all of them in summer, since a garden hose moves 15–20 litres a minute.
Does a low-flow shower head actually save money?
It saves twice, because it cuts both the water and the energy needed to heat it. Dropping from 9 to 6 litres per minute reduces an 8-minute shower from 72 to 48 litres, and for four daily showers that is around $260 a year across water and heating at typical prices.
How much water does a leaking toilet waste?
A silently running flapper can pass 200 to 500 litres a day, which is 70 to 180 cubic metres a year — more than a whole family's showers. It is the single cheapest thing to check: put dye in the tank and look at the bowl after twenty minutes without flushing.