How Much Hot Water Does a Shower Use?

Short answer: most Australian showers use 6–15 litres per minute. Over 5–10 minutes that’s about 30–150 litres of mixed water. Of that, around 40–60% is hot water drawn from your system (higher in winter, lower in the tropics). As a rule of thumb, an 8‑minute shower with a 9 L/min head uses ~72 L of mixed water and roughly 36–43 L of hot water from the tank depending on season.

What counts as “hot water” in a shower?

Two volumes matter:

• Total mixed water: what you see at the shower — cold and hot blended to about 38–42°C.
• Hot water drawn from the system: the litres of 60°C water (from a storage tank) or heated outlet (from an instantaneous unit) needed to make that mixed water.

In Australia, stored water must be kept at 60°C to control Legionella, and bathrooms are limited to a 50°C maximum delivery via a tempering valve. Most people shower around 40°C.

The proportion of your shower that comes from the hot water system depends on the incoming cold-water temperature. A simple way to estimate the hot fraction is:

Hot fraction ≈ (40°C − cold inlet °C) ÷ (60°C − cold inlet °C)

That works because stored 60°C water is tempered to 50°C before it reaches the bathroom, then your shower mixer blends to ~40°C. The maths collapses neatly to the formula above.

• If your cold inlet is ~20°C (typical warm-season mains), hot fraction ≈ (40−20)/(60−20) = 0.5 → about half the shower is hot water from the tank.
• If cold inlet is ~10°C (southern winters), hot fraction ≈ 30/50 = 0.6 → about 60% hot.
• If cold inlet is ~25°C (tropical conditions), hot fraction ≈ 15/35 ≈ 0.43 → about 43% hot.

How much hot water does a “normal” shower use?

First, find your flow rate. Look for the WELS star label on the shower head or do a quick bucket test (see tip below). Then multiply by minutes.

• Efficient head (7.5 L/min), 5-minute shower: 37.5 L mixed. Hot water used ≈ 19 L at 20°C inlet, ≈ 23 L at 10°C inlet.
• Common modern head (9 L/min), 8-minute shower: 72 L mixed. Hot water used ≈ 36 L at 20°C inlet, ≈ 43 L at 10°C inlet.
• Older head (12 L/min), 10-minute shower: 120 L mixed. Hot water used ≈ 60 L at 20°C inlet, ≈ 72 L at 10°C inlet.

If you have a continuous-flow (instantaneous) gas unit, you don’t “use up” a tank — the unit just heats whatever flow you call for. The mixed litres are still flow × minutes, and the hot fraction logic above still tells you how hard the heater has to work (bigger temperature rises in winter mean lower available L/min at a set outlet temperature).

Energy and cost per shower

Heating water is one of the biggest energy loads at home. You can estimate the energy for a shower using the hot litres you just worked out.

The quick way

• Electric storage (resistive): kWh ≈ hot litres × (60 − cold inlet °C) × 0.001163. Example: 36 L hot, 20°C inlet → 36 × 40 × 0.001163 ≈ 1.67 kWh.
• Heat pump: Take the electric storage result and divide by the COP (often 2–3). Example: 1.67 kWh ÷ 3 ≈ 0.56 kWh.
• Gas: First find the equivalent heat in kWh (as above), then convert to MJ and allow for efficiency. MJ ≈ kWh × 3.6 ÷ efficiency. Example: 1.67 kWh × 3.6 ÷ 0.8 ≈ 7.5 MJ.

To turn that into dollars, multiply by your tariff: electricity in $/kWh, gas in $/MJ. Tariffs vary widely by state and retailer, and many electric storage systems run on cheaper controlled-load (off‑peak) rates. Check your bill.

Things that swing the numbers

• Season: Colder inlet water in winter means a higher hot fraction and more energy per litre.
• Flow and time: Every extra minute at 9 L/min adds 9 L mixed and typically another 4–6 L of hot water.
• Set temperatures: You must store at 60°C. Bathroom delivery is limited to 50°C by the tempering valve. Comfortable showers are ~38–42°C.

How many back‑to‑back showers can my system do?

Storage systems are sold in familiar sizes: 125 L, 160 L, 250 L, 315 L, 400 L. Because you mix in cold water, each litre of 60°C storage yields more than a litre of usable 40°C shower water.

A handy rule: with a 20°C inlet, hot fraction is ~0.5, so each 1 L of 60°C storage yields ~2 L of 40°C mixed water. With a 10°C inlet, each 1 L yields ~1.67 L of 40°C water.

• 125 L storage: about 250 L of 40°C mixed in mild conditions (≈3–4 efficient 8‑minute showers at 9 L/min). In winter (~10°C inlet), around 210 L (≈3 showers).
• 250 L storage: about 500 L mixed in mild conditions (≈6–7 efficient showers), or ~420 L in winter (≈5–6 showers).

Real‑world results depend on recovery: the burner or element reheats as you shower. Gas storage and heat pumps recover faster; small electric elements on off‑peak may not recover until the next tariff window. If you regularly run out, consider:

• Shortening showers or fitting a lower‑flow head.
• Shifting electric storage to off‑peak plus a daytime boost if you have solar PV (talk to a licensed electrician/plumber).
• Upsizing the tank or switching to a heat pump or high‑capacity continuous‑flow gas (see our system sizing guide).

How to measure and reduce your shower’s hot water use

Measure yours

1. Find your flow: Do the 10‑second bucket test and multiply by 6.
2. Pick your temperatures: Assume 40°C at the shower. Estimate cold inlet from season/location: southern winters 10–15°C, summers 18–22°C; northern Australia 20–30°C.
3. Work out volumes: Mixed litres = flow × minutes. Hot fraction = (40 − cold) ÷ (60 − cold). Hot litres ≈ mixed × hot fraction.
4. Estimate energy: For storage electric, kWh ≈ hot L × (60 − cold) × 0.001163. For heat pumps divide by COP; for gas convert to MJ and allow for efficiency.

Cut the waste

• Upgrade the shower head: A 9 L/min head to a 7.5 L/min (or 6 L/min) can save 10–35 litres per shower and the energy that goes with it. Look for 4–5 star WELS.
• Time it: Dropping from 8 to 5 minutes at 9 L/min saves 27 litres mixed and roughly 13–16 litres of hot water.
• Fix drips and warm‑up habits: Collect cold run‑off in a bucket for plants while you wait for hot water to arrive.
• Use off‑peak wisely: If you have electric storage, ask your retailer about controlled‑load tariffs; see our guide to off‑peak hot water.
• Solar and heat pump: If you have solar PV, consider heating during the day; many heat pumps have timers. Get a licensed plumber/electrician to set this up.

Note: Don’t turn a storage system below 60°C — it’s a safety requirement. Bathroom delivery should be limited to 50°C via a tempering valve. If your shower is scaldy or tepid, have a licensed plumber check the valve and thermostat.

What about continuous‑flow units?

With gas continuous‑flow, capacity is stated as litres per minute for a given temperature rise. In winter (bigger rise from cold to set temperature), the available L/min falls. If your unit struggles with two showers at once, try reducing the shower flow rate or set the unit to 50°C and run the shower mixer closer to full hot to reduce cold mixing losses. For persistent issues, see our guide to sizing a hot water system.

Bottom line: the quickest wins are a better shower head and a shorter shower. Measure your flow, do the sums, and you’ll know exactly how much hot water your shower uses — and what it’s costing you.