Where hot water money quietly disappears

Heating water is one of the largest single uses of energy in a typical UK home, accounting for roughly a fifth of the average gas bill. Because it happens out of sight — inside a cylinder, a combi boiler or a pipe run under the floorboards — it rarely gets the attention that radiators and thermostats do. But the waste adds up through a handful of well-worn routes: water stored hotter than it needs to be, pipes losing heat before it reaches the tap, a dripping hot tap that runs all day, and a shower head that quietly pours 12 litres a minute down the drain.

The good news is that most of these are cheap or free to put right. Here is a practical order of attack, from the quickest wins to the slightly bigger jobs worth planning in.

Turn the cylinder thermostat down — but not too far

If you have a hot water cylinder, its thermostat is probably set somewhere between 65°C and 70°C, often from habit rather than need. Stored water must be kept at at least 60°C to keep legionella bacteria under control, so 60°C to 65°C is the sensible band. Dropping from 70°C to 60°C means the cylinder loses less heat every hour it stands, and you also waste less energy overheating water that gets mixed back down with cold at the tap anyway.

• Set the cylinder thermostat to 60°C and leave it there.
• Make sure the thermostat is not buried under a cylinder jacket or a pile of stored items — it has to sense the water, not the air.
• Set the boiler's own flow temperature around 10°C higher than the cylinder thermostat so the cylinder can actually reach its target.
• If you have a combi boiler, simply set the hot water temperature dial to the lowest point that still gives you a comfortable shower, often around 50°C.

If your cylinder is heated by an immersion heater, use the built-in timer rather than leaving it on constantly, and heat the tank only before the times you actually need hot water.

Spend less on showers and running taps

A bath uses around 80 litres. A ten-minute shower under a 12 litre-per-minute head uses 120 litres — so "quick shower" is not automatically the frugal option. An aerated or low-flow shower head, typically £15 to £40, mixes air into the water so the spray still feels brisk at 8 litres a minute or less. Some water companies give these away free, so it is worth a look before you buy.

• Fit a flow restrictor or a regulated shower head rather than relying on willpower alone.
• Time your showers for a week. Most people find they are two or three minutes longer than they guessed.
• Wash up in a bowl rather than under a running hot tap, and use cold water for rinsing vegetables.
• Run washing machines and dishwashers on eco or 30°C cycles, and only when full.

Lag everything that carries heat

Heat lost from pipework and cylinders is paid for twice: once when the water is heated, and again when the boiler fires to replace it. If your cylinder feels warm to the touch, it is under-insulated. A well-fitted jacket of at least 80mm — usually £15 to £25 and a twenty-minute job — can save a meaningful slice of water-heating costs each year. Cylinders made after the mid-1990s usually have factory foam insulation, but even those can benefit from a top-up jacket.

• Lag the first metre of hot pipe leaving the cylinder, and the primary pipework running between the boiler and the cylinder.
• Lag hot pipes anywhere they pass through cold spaces such as lofts, garages and under suspended floors.
• Do not lag over the cylinder thermostat or any safety valve — leave those clear.

Fix drips and leaks promptly

A hot tap dripping once a second can waste more than 5,000 litres a year, and every drop of it was heated by your boiler or immersion. That is a few pounds a year in water and a similar amount again in energy, for a repair that often costs pennies in washers. The same applies to a constantly running overflow from a loft tank, a leaking shower mixer, or a ball valve that never quite shuts off. If you can hear water moving when nothing is in use, investigate it.

It is also worth checking whether your hot water cylinder is losing heat through a poorly fitting immersion boss or an unlagged flange — small gaps let warm air escape steadily.

Sensible habits and upgrades to plan in

Once the basics are sorted, a couple of larger improvements are worth considering if you are already having work done. A drain-water heat recovery unit, fitted under a shower tray, uses the warm waste water to pre-heat the cold supply going back into the shower — it typically costs a few hundred pounds and suits anyone redoing a bathroom. If your kitchen tap is a long way from the cylinder, a small point-of-use water heater under the sink can save you running several litres of water down the drain while you wait for it to warm up.

None of this requires a major renovation. Set the cylinder to 60°C, fit a better shower head, lag the pipes and fix the drips this weekend — and you will have quietly trimmed one of the most stubborn lines on your energy bill.