Most advice on saving water at home focuses on fixtures: low-flow shower heads, aerators, dual-flush toilets. Those help, and they are worth fitting.
But a substantial share of the water and energy a household wastes never reaches a fixture at all. It is lost in the system behind them, through excessive pressure, water run down the drain waiting for hot to arrive, and heat leaking from pipes and cylinders. Those losses are addressed by components rather than by fittings, and they are largely invisible.
This guide covers where those losses occur, which components address them, and how they rank by effect.
Where Water and Energy Are Actually Lost
| Loss | What it costs | Addressed by |
|---|---|---|
| Water run while waiting for hot | Treated water discarded, every time | Recirculation valve |
| Excessive supply pressure | More water per second at every outlet | Pressure limiting valve |
| Cylinder standby losses | Heat lost continuously, day and night | Insulation, correct set temperature |
| Pipe heat loss | Heat lost between cylinder and tap | Pipe insulation |
| Inefficient heat source | Energy conversion at 1:1 rather than 4:1 | Heat pump water heating |
| Overheating rooms | Heating space nobody occupies | Zone control and thermostats |
| Undetected leaks | Continuous, often for months | Pressure monitoring |
The Waste Nobody Measures: Waiting for Hot Water
This is the largest single water loss in most homes, and it happens several times a day without anyone noticing.
When a hot tap is closed, the water sitting in the pipe between the cylinder and that tap cools to room temperature. The next time the tap opens, all of that cooled water must run down the drain before hot water arrives.
How long depends on pipe length. A bathroom near the cylinder delivers hot water in seconds. A bathroom at the far end of a house, or on an upper floor, can take well over a minute. Every second is treated water, pumped and paid for, discarded unused.
Multiply it across a household. Several people, several outlets, several times a day, every day. In a home with long pipe runs, the water discarded while waiting for hot adds up to a substantial annual volume, and it is the one loss that produces nothing at all in return. It is not water used inefficiently; it is water not used.
The component that addresses it
A water return system control valve sits at the far end of a hot water loop. When the water there has cooled, a wax thermostatic element inside contracts and the valve opens, allowing that cooled water to return toward the heater and drawing hot water forward through the loop. When hot water arrives and the temperature rises, the element expands and the valve closes.
The result is hot water at the tap within seconds rather than after a long flush, and no water discarded.
Two honest qualifications. Keeping a loop warm means the pipe loses heat continuously, so the loop must be insulated or the energy saved by not reheating flushed water is exceeded by standing losses. And a thermostatic valve is considerably better than a pump running continuously, because circulation happens only when the loop has actually cooled.
Excessive Pressure Wastes Water Continuously
Supply pressure varies enormously between networks and rises overnight when demand falls. Household fixtures are designed to work well at moderate pressure, and where incoming pressure substantially exceeds that, several things follow.
More water leaves every open tap per second. The same handwash, the same shower duration, more litres consumed. This happens at every outlet, every time, with no change in behaviour and no benefit.
Seals wear faster. Tap washers, appliance inlet valves, and pipe joints all face greater stress. Repeated seal failures across several fixtures usually indicate pressure rather than a quality problem with the fittings.
Appliance hoses fail sooner. Washing machine and dishwasher inlet hoses are permanently pressurised, and a burst hose under mains pressure discharges a considerable volume very quickly.
A pressure limiting valve reduces incoming pressure to a controlled level and holds it there. Water consumption falls directly as a consequence, and everything downstream lasts longer.
Before fitting one, measure. A pressure gauge screwing onto an outside tap costs very little and tells you whether you have a problem worth addressing.
Standby Losses and Insulation
A hot water cylinder loses heat through its walls continuously, whether or not anyone uses hot water. That loss occurs every hour of every day, including in an empty house.
Modern cylinders are better insulated than older ones, and adding a jacket to a poorly insulated cylinder is among the cheapest energy measures available.
Pipe insulation addresses the same loss in the distribution. It does not make water heat faster, which is sometimes claimed. What it does is reduce heat escaping from the pipe, so water arrives at the tap hotter and stays hot longer in the pipe between uses, which shortens the wait next time.
Insulating the first few metres from the cylinder gives the greatest return for the least effort, since that pipework is hottest and loses most.
Where a recirculation loop exists, insulating it is not optional but essential, since an uninsulated loop kept warm continuously loses heat around the clock.
The Heat Source: The Largest Energy Factor
Everything above concerns losses. The heat source determines how efficiently the energy that is used gets converted in the first place, and the differences here are larger than anywhere else in the system.
An electric immersion element converts electricity to heat at exactly one to one. Every unit purchased becomes one unit of heat, and no product improvement changes that, because it is the physical limit of resistive heating.
A heat pump delivers three to four units of heat for the same electricity, because it moves heat that already exists in the air rather than generating it.
Legom air-to-water heat pumps produce domestic hot water alongside space heating:
| Unit | Hot water capacity | Water yield | COP |
|---|---|---|---|
| 5 kW | 6 kW | 129 L/h | 4.4 |
| 6 kW | 8 kW | 172 L/h | 4.3 |
| 9 kW | 10 kW | 215 L/h | 4.32 |
| 16 kW | 18 kW | 387 L/h | 4.35 |
All models use R32 refrigerant, with a global warming potential of 675 against 2088 for the older R410A, and requiring a smaller charge for the same output.
On refrigerants and what “eco-friendly” means
Worth addressing directly, because it is commonly misunderstood.
R410A is not an environmentally friendly refrigerant. It was an improvement on R22, which is why it was widely adopted, but with a GWP of 2088 it is now itself subject to progressive quota restriction under the European F-Gas Regulation and equivalent rules elsewhere.
The practical consequence for anyone buying equipment is commercial as well as environmental: as quotas tighten, refrigerant charged under restriction becomes harder and more expensive to obtain, which makes servicing that equipment progressively costlier regardless of its mechanical condition.
Heating Control: Not Heating What Nobody Uses
On the space heating side, the largest avoidable waste is heating rooms that are empty.
Zone control allows unused rooms to go unheated and bedrooms to run cooler than living areas. In a multi-room property this removes more waste than any scheduling adjustment, because a room heated to a temperature nobody experiences is entirely wasted energy.
In a hydronic system this requires a manifold with a thermal actuator on each circuit and a room thermostat per zone, coordinated by a base station.
Lowering the flow temperature costs nothing where the emitters can still deliver enough output. A condensing boiler only condenses when return water is below roughly 55°C, and a heat pump becomes markedly more efficient as required flow temperature falls. Turning the setting down recovers efficiency already paid for.
Fixtures: Genuinely Useful, Honestly Framed
Low-flow shower heads, tap aerators, and dual-flush toilets all reduce consumption, and they are worth fitting. Two points are worth making accurately.
Low flow does not mean weak. Older restricted heads simply reduced pressure, producing a poor shower. Modern designs use smaller apertures and mix air into the stream, so perceived pressure remains good while volume falls.
They do not heat water. A shower head is a fitting, not a heater. What reduced flow does is lessen the volume of hot water drawn, which reduces the energy the heater must supply. The saving comes from using less hot water, not from the fitting doing anything to the water’s temperature.
Legom does not manufacture shower heads, taps, or sanitary fittings. Our range covers the system components behind them: valves, thermostats, actuators, manifolds, pipe, heat pumps, and purification. Where fixtures are concerned, buy them from a sanitaryware supplier.
Leaks: The Loss That Runs Continuously
A leak wastes water every hour until it is found, and hidden leaks frequently run for months.
The most reliable indicator in a sealed heating system is falling pressure. A system that holds its pressure has no leak; one needing regular topping up does.
On the mains side, a sudden increase in water consumption with no change in usage points to a leak somewhere, and the standard test is to close every outlet and check whether the meter still moves.
Checking system pressure periodically and noting the reading catches a slow leak early, when it is a small repair rather than a floor to lift. Our guide to underfloor heating and hydronic leaks covers diagnosis in detail.
Ranked by Effect
Not everything on this list matters equally, and the order is worth knowing before spending.
1. The heat source. Moving from resistive electric heating to a heat pump changes the conversion ratio from one to one to roughly four to one. Nothing else on this list approaches that.
2. Zone control and flow temperature. Not heating unoccupied space, and running the system at the lowest temperature the emitters allow. Lowering flow temperature costs nothing at all.
3. Insulation. Cylinder and pipe insulation reduce a loss that occurs continuously, and both are inexpensive.
4. Pressure limiting. Reduces consumption at every outlet and extends the life of everything downstream.
5. Recirculation control. Eliminates water discarded waiting for hot, provided the loop is insulated.
6. Fixtures. Genuinely useful, cheap, and easy, but smaller in effect than the items above.
7. Leak monitoring. Costs nothing and prevents a loss that would otherwise run indefinitely.
“The saving people never account for is water run down the drain waiting for hot to arrive. It happens several times a day in every household with a long pipe run, and it produces nothing at all, because that water was never used. A thermostatic recirculation valve fixes it, but the thing I always add is that the loop has to be insulated. Keep a bare pipe warm all day and you have solved a water problem by creating an energy one. Insulated, it works. Uninsulated, you are heating the airing cupboard.”
— Maggie Shen, Director of Legom
Components from Legom
Legom manufactures the system components that address these losses, at our facility in Jiaxing, Zhejiang Province, supplying partners in more than 90 countries.
The HVAC valve range covers pressure limiting valves, water return system control valves, thermostatic mixing valves, and temperature and pressure relief valves. Alongside these we produce air-to-water heat pumps, floor heating pipe with oxygen barrier protection, manifolds, thermal actuators, room thermostats, and air and water purification.
Because we also produce the wax thermostatic elements inside these valves, switching characteristics are specified at the source, with every element tested and rated for 100,000 operating cycles.
OEM and ODM services are available across the range. Contact the technical team to discuss specification for a project.
Frequently Asked Questions
What wastes the most water in a hot water system?
Water run down the drain while waiting for hot to arrive, in most homes with long pipe runs. When a hot tap is closed, the water in the pipe cools, and next time all of it must be flushed before hot arrives. It happens several times a day, and unlike inefficient use it produces nothing at all. A thermostatic recirculation valve at the far end of the loop addresses it, provided the loop is insulated.
Does high water pressure waste water?
Yes, continuously and invisibly. More water leaves every open tap per second, so the same handwash or shower duration consumes more litres with no behavioural change and no benefit. High pressure also wears seals faster, shortens appliance inlet valve life, and stresses pipe joints. A pressure limiting valve reduces incoming pressure to a controlled level. Measure first with an inexpensive gauge to establish whether you have a problem worth addressing.
Do low-flow shower heads reduce water pressure?
Older restricted designs did, which is where the reputation comes from. Modern low-flow heads use smaller apertures and mix air into the stream, so perceived pressure stays good while volume falls. What they do not do is heat water: a shower head is a fitting, not a heater. The energy saving comes from drawing less hot water, so the heater supplies less, rather than from the fitting affecting water temperature.
Does pipe insulation make water heat faster?
No, and this is commonly misstated. Insulation does not add heat or accelerate heating. What it does is reduce heat escaping from the pipe, so water arrives at the tap hotter and stays warm longer between uses, which shortens the wait next time. Insulating the first few metres from the cylinder gives the greatest return, since that pipework is hottest. On a recirculation loop, insulation is essential rather than optional.
Is R410A an eco-friendly refrigerant?
No. It was an improvement on R22, which is why it was widely adopted, but with a global warming potential of 2088 it is now itself subject to progressive quota restriction under the European F-Gas Regulation and equivalent rules elsewhere. R32, at 675 and requiring a smaller charge for the same output, is the current lower-GWP alternative. The consequence is commercial as well as environmental: restricted refrigerants become harder and more expensive to obtain as quotas tighten.
What is the single biggest energy saving in a hot water system?
The heat source. An electric immersion element converts electricity to heat at exactly one to one, which is the physical limit of resistive heating. A heat pump delivers three to four units of heat for the same electricity, because it moves existing heat rather than generating it. Nothing else on the list of water and energy measures approaches that ratio. After the heat source, zone control and lowering flow temperature come next.
Does Legom sell shower heads and taps?
No. Legom manufactures the system components behind fixtures: HVAC valves including pressure limiting, recirculation, and mixing valves, air-to-water heat pumps, floor heating pipe, manifolds, thermal actuators, room thermostats, and air and water purification. Shower heads, taps, and sanitary fittings are not part of our range and should be sourced from a sanitaryware supplier.
In a sealed heating system, falling pressure is the indicator. A system that holds pressure has no leak; one needing regular topping up does, and repeatedly refilling makes matters worse because each top-up introduces oxygen that corrodes components internally. On the mains side, close every outlet and check whether the water meter still moves. Checking pressure periodically catches a slow leak while it is still a small repair.
Reviewed by Maggie Shen, Director at Legom, on September 1, 2026. This guide to water and energy saving in hot water systems was reviewed for accuracy, including the function of pipe insulation, refrigerant global warming potential figures, and the scope of Legom’s product range.