Hot water systems waste energy through long showers, high-flow fixtures, leaks and ageing units. Measure your baseline, fix habits and fixtures, then replace the system when conserving stops working. A licensed plumber can supply and install same-day where available.
This page provides general guidance. For diagnosis of hot water faults or fixture installation, consult a licensed plumber in your state.
Heating water accounts for 15-30% of an average Australian household’s energy use, according to the Australian Government. The cost of your hot water comes down to one formula.
| Litres of hot water | × Temperature rise (°C) | × 0.001163 | ÷ System efficiency | = Energy (kWh) |
| How much hot water you use | Hot temperature minus cold temperature | Energy to heat 1 L by 1°C | Close to 1 for an electric element | What you pay to heat it |
0.001163 is how much energy, in kilowatt-hours, it takes to heat 1 litre of water by 1 °C. You don’t need to work it out; just use it as it is.
The last part of the formula, efficiency, depends on your system:
For example, consider a household of four, each using 50 litres of hot water a day, heated from 15°C to 60°C (a rise of 45 °C). These are example numbers, not averages, so swap in your own.
| Step | Calculation | Result |
| Daily litres | 4 people × 50 L | 200 L |
| Daily energy | 200 L × 45°C × 0.001163 | About 10 kWh per day |
| Yearly energy | About 10.5 kWh × 365 days | About 3,800 kWh per year, before system losses |
Multiply the kWh by the cents per kWh on your electricity or gas bill to get your heating cost. Your water utility also charges per kilolitre for the same litres. That charge is separate from, and on top of, the energy cost.
Before you change anything, work out your own starting point.
For example, if 4.5 litres collects in 30 seconds, your shower runs at 9 litres a minute. An 8-minute shower then uses 72 litres of mixed hot and cold water.
Some changes cost nothing and cut your hot water use: shorter showers, cold washes, full loads, and spreading out your heavy use. Each one means your system has to supply less hot water.
Yes, by lowering the flow each minute. Hot water saved = flow reduction (L/min) × minutes × hot share. Check the WELS star rating before buying, and have a licensed plumber fit the fixture.
WELS is the Water Efficiency Labelling and Standards scheme. It gives a star rating and flow rate for taps, showers, dishwashers, and washing machines so that you can compare products on one scale.
| Fixture | Rating and flow | Effect on hot water use |
| Showerhead, 3 star | Up to 9 L/min | Baseline for many older showers |
| Showerhead, 4 star | About 6 to 7.5 L/min | Lower flow per minute |
| Showerhead, 5 star | About 4.5 to 6 L/min | Lowest flow rated |
| Basin tap, 6 star | 4.5 L/min or less | Cuts hot draw at every hand wash |
| Dishwasher and washing machine | WELS label shows litres per cycle | A cold cycle on a washing machine removes hot draw entirely |
Say you swap a 9 L/min showerhead for a 6 L/min one, and you shower for 8 minutes.
A plumber can fit a new showerhead or tap part and check that it suits your water pressure and your system.
Generally not for storage tanks. Stored water is kept at 60°C or above to limit Legionella growth, so lowering the thermostat can create a health risk. Reduce your hot water use instead.
What the tank has to do. Legionella is a bacterium that grows in warm water and can cause a serious lung infection. The Plumbing Code of Australia requires storage water heaters to hold water at 60°C or hotter, with some exceptions for systems designed to manage the risk another way.
What comes out of your taps. That’s a different story. For most homes, the code limits bathroom hot water to 50°C so it doesn’t scald. A tempering valve does that by blending cold water into hot water as it leaves the system. The tank stays hot, and the taps stay safe.
What a tempering valve doesn’t do. It protects you from burns, but it won’t cut your energy use. To do that, turn down the litres, not the thermostat.
Heat pumps, solar, and continuous-flow systems work differently from a standard storage tank, so ask a licensed plumber what applies to yours before you change any setting.
The Plumbing Code of Australia sets the rules, and each state regulator applies them; some building types have stricter limits. Check with your state regulator or a licensed plumber before changing any thermostat.
Losses differ by system type. Storage tanks lose heat while idle, continuous flow units have a start-up delay, and heat pumps are rated by efficiency. Compare individual models on one stated metric, not the system type alone.
| System type | Where heat or water is lost | Metric to compare |
| Electric storage | Heat through the tank wall while idle. This grows with tank size and shrinks with better insulation. | Standby loss figure on the manufacturer’s data sheet |
| Gas storage | Standby loss, plus heat lost up the flue | Manufacturer’s efficiency figure |
| Gas continuous flow | No stored water, so no standby loss. Water runs cold briefly at start-up, and a minimum flow is needed to ignite. | Manufacturer’s thermal efficiency and minimum activation flow |
| Heat pump | Efficiency varies with the model and the conditions | COP per model, from the data sheet |
| Solar with booster | The booster runs on low-sun days | Manufacturer’s stated solar contribution |
A bigger tank is not a free upgrade. A larger tank has more surface area, so it loses more heat while idle.
Hot water that’s hot but costs a lot usually points to habits. Lukewarm water, no hot water, a constant drip, or water coming from the tank or relief valve points to a fault. A licensed plumber can confirm which.
| Symptom | Likely cause | Repair or replace | Next step |
| Constant drip from a hot tap | Worn tap component | Repair | Licensed plumber |
| Water runs out quickly or is only lukewarm | Failing element or thermostat, or a tank too small for the household | Repair, or replace if it keeps happening | Licensed plumber or electrician |
| No hot water at all | Electric: power, thermostat or element. Gas: pilot or ignition. | Depends on the fault | Licensed tradesperson |
| Circuit breaker keeps tripping | Possible short circuit in an element | Stop using the unit | Licensed tradesperson, straight away |
| Water discharging from the pressure relief valve | A faulty valve, or normal expansion while the tank heats | Valve repair is possible | Plumber to confirm. Never block the valve. |
| Water leaking from the tank body | Failed tank | Replace | Licensed plumber |
Some intermittent discharge while a tank is heating is common, but constant discharge is not. A tank body leak is the clearest sign: it cannot be repaired.
Replace when the tank body leaks, repairs keep recurring, the unit is the wrong size for the household, or it can no longer hold temperature. A licensed plumber can confirm whether to repair or replace.
If none of these applies, stick with the habit and fixture changes above.
We supply and install the hot water system, so you deal with one team instead of sourcing a unit and a plumber separately. We can do it the same day if local stock is available, our crew’s available, and the booking cut-off time is met. The final price depends on the system you choose, its capacity and where you live. To check availability and get a quote, call 1300 721 996.
It varies with the household, and we haven’t found a reliable single Australian figure. Measure your own: time your showers, count your hot loads, then run the baseline formula above.
Yes. At illustrative inputs, two minutes less saves about 10 L of hot water and about 0.5 kWh. Multiply by your shower count and your cents per kWh.
Usually the tank is too small for your household’s peak use, or an element or thermostat is failing. A licensed plumber can tell which.
Not safely on a storage tank, which must stay at 60°C or above. Instead, cut hot water use with shorter showers and efficient fixtures.
Often, depending on local stock, crew and the booking cut-off. Call 1300 721 996 to check availability for your area.