Hot water savers: the four kinds, and which one suits your house
The water you run down the drain waiting for hot is decided by the distance between the heater and the tap. Most devices sold to fix that are managing the symptom, and they manage different ones.
A “hot water saver” is not one product. The phrase is attached to at least four quite different devices that solve different problems. The one most people are actually looking for deals with a specific and very ordinary annoyance: the cold water you run down the drain while waiting for hot water to reach the tap.
That water is not wasted because the system is inefficient. It is wasted because of geometry. Every time hot water stops flowing, whatever is left in the pipe between the heater and the tap sits there and cools. And the next time you open the tap you have to push all of it out before hot arrives.
Plumbers call that column the dead leg. Its volume is decided by the length and the diameter of the pipe run, not by the brand of your hot water system and not by how patient you are.
Understanding that changes which product makes sense, because three of the four kinds of hot water saver do not reduce the dead leg at all. They deal with its consequences in different ways.
What are the four kinds of hot water saver?
| Type | What it actually does | What it needs |
|---|---|---|
| Diverter or water recovery | Catches the cooled water that would otherwise go down the drain and sends it somewhere useful instead. The water is saved rather than the wait | A licensed plumber, a return line back from the tap end, and somewhere for the recovered water to go |
| Recirculation or pre-heat | Moves the cooled water out of the pipe before you open the tap, so hot arrives almost immediately. The wait is removed rather than the water saved | A compatible hot water system, a control or button, and in most arrangements a dedicated pipe run |
| Flow reduction | Reduces how much hot water leaves the outlet in the first place: efficient showerheads, tap aerators, flow restrictors. Does nothing about the dead leg, but reduces everything after it | Usually nothing beyond fitting the outlet, which is the one category with a genuine DIY component |
| Timers and behaviour | Shower timers and similar. Changes how long the hot water runs, which is a real saving but a different one entirely | Nothing structural |
Those are not competing answers to the same question. A diverter and an efficient showerhead save water in completely different places, and a household with a long pipe run to the bathroom may reasonably want both.
How the diverter approach works
The Australian example most people encounter is the Redwater Diverter, which was invented and is made in Australia. The manufacturer states that it needs no electricity, that it can be retrofitted into existing plumbing or built into new work. And that it is certified to Australian Standard AS 1357.2. Installation involves a plumber fitting the unit and running a return line, and the recovered water is then available to be used rather than drained.
The appeal is obvious in a house on tank water or under water restrictions, where the water itself is the thing you are trying not to lose. The limitation is equally obvious: it is a plumbing alteration, it needs a physical return path from the far end of the run. And how practical that is depends entirely on how your house is built. A single-storey house on a slab and a two-storey house with a bathroom above a garage are very different propositions.
How the recirculation approach works
Recirculation answers the other half of the complaint. Instead of saving the cold water, it gets it out of the way before you want the tap, so hot water is there when you turn it on.
Rinnai sold an accessory of this kind in Australia for its Infinity continuous flow units, the Smartstart Water Saver, operated by a pre-heat button on the water controller or by a manual switch.
It is worth knowing that Rinnai now lists that product as discontinued, which is a useful illustration of a wider point: accessories in this category come and go. And what a plumber can actually source and support today is a better guide than an article or a forum post from a few years ago. Ask what is currently available for your specific unit rather than asking for a product by name.
The important constraint with any recirculation arrangement is that it is tied to the hot water system itself. Whether it is possible at all, and what it would need, depends on what you have installed: and the answer is different for a continuous flow unit than for a storage tank.
Why the pipe run decides more than the device
This is the part the product pages do not lead with. Suppose the bathroom is a long way from the hot water unit, or the pipe serving it is larger in diameter than it needs to be. Then the dead leg is large, and every device in the table above is managing a problem created by the layout.
Which matters because there are moments when the layout is actually available to change, and those are the moments worth spending on:
- When the hot water system is being replaced. Where the new unit goes is decided at that point, and moving it closer to the outlets that get used most is a permanent fix rather than a workaround. It is worth raising before the install, not after.
- When a bathroom or kitchen is being renovated and the pipework is open anyway.
- When an outlet is a long way from everything else. A separate small unit serving just that outlet removes the dead leg entirely, because there is barely any pipe left between heater and tap.
- Insulating the hot water pipe. This does not shrink the dead leg, but it slows how fast the water in it cools, so on a normal day the pipe is still warm and the wait is shorter. Where the pipe is accessible, it is among the least glamorous and best-value things you can do.
Sizing the unit correctly matters here too, for a slightly different reason: an oversized system in the wrong spot does not fix a wait, it just holds more water further away. What size hot water system you actually need covers that judgement.
What if the wait has got worse recently?
A dead leg is constant. If the wait has noticeably lengthened, or the pressure behind it has dropped, that is a change rather than a design limitation. And it is a different problem with different causes. See low hot water pressure. Similarly, if hot water arrives and then goes lukewarm, no saver device addresses that; lukewarm hot water is usually a valve or a thermostat.
The least exotic saving of all is a tap that drips hot water. It loses heated water continuously, day and night, and over a year that comfortably outweighs what any of these devices recover. A dripping tap is worth fixing before buying anything.
What is genuinely yours to do
- Measure the problem before buying a solution. Put a bucket under the shower, run it until the water is properly hot, and see how much you actually collected. That single number tells you whether this is worth solving at all, and it is the number to quote when you ask a plumber.
- Work out where the hot water unit is in relation to the outlet that annoys you. The distance is the cause.
- Look at the star rating on your showerhead. Australian tapware and showers carry a water efficiency rating, and an old showerhead is often the single largest hot water consumer in the house.
- Use the water rather than engineering it away. The cheapest diverter is a bucket under the tap while the water warms, used on the garden or for cleaning. It is not elegant, but it recovers the same water as a device does.
- Insulate accessible hot water pipe, particularly in a roof space or under the floor.
- Raise it before the next system replacement, which is the only moment the location is genuinely on the table.
Frequently asked questions
What is a hot water saver?
It is not one product. The name is used for at least four different things: diverters that capture the cooled water in the pipe so it is not lost down the drain, recirculation or pre-heat systems that clear that water before you open the tap so hot arrives quickly, flow reduction fittings such as efficient showerheads and aerators, and timers that simply shorten how long the hot water runs. They save different things, and they are not alternatives to each other.
Why do I have to wait so long for hot water?
Because of the water sitting in the pipe between the heater and the tap. Once hot water stops flowing, that column cools down, and the next time you open the tap you have to push all of it out before hot arrives. Plumbers call it the dead leg, and how much there is depends on the length and diameter of the pipe run rather than on the hot water system itself.
Does a hot water saver reduce my water use or just the waiting?
It depends which kind. A diverter saves the water but you still wait, because it captures the cooled water and redirects it somewhere useful. A recirculation or pre-heat system removes the wait but does not by itself save that water, it moves it. Flow reduction fittings reduce consumption everywhere but do nothing about the dead leg. Being clear about which of those two problems bothers you most is the useful first step.
Can I install a hot water saver myself?
Not the plumbed ones. Diverters, return lines and recirculation pipework connect into the water supply, which is licensed plumbing work in every Australian state and territory and must comply with the plumbing provisions of the National Construction Code. Incorrect cross-connections are one of the main things those rules exist to prevent. Replacing a showerhead or fitting a tap aerator is the part that is ordinarily yours.
Is insulating the hot water pipe worth it?
Where the pipe is accessible, it is one of the better-value things you can do. It does not make the dead leg any smaller, but it slows how quickly the water in the pipe cools, so in normal daily use the pipe is more often still warm and the wait is shorter. Roof spaces and underfloor runs are the usual places it is both worthwhile and reachable.
What is the cheapest way to stop wasting water waiting for hot?
A bucket under the tap while the water warms up, used afterwards on the garden or for cleaning. It recovers the same water a diverter does without any plumbing at all. It is worth doing that for a week first, because it also measures the problem: if the bucket barely fills, an installed device is unlikely to be worth it for your house.
Would moving the hot water system closer fix the wait?
Yes, and it is the only genuine fix rather than a workaround, because it shortens the pipe run that causes the problem. The catch is that it is only practical at particular moments, principally when the system is being replaced anyway or a bathroom is being renovated. For an outlet a long way from everything else, a separate small unit serving just that outlet achieves the same thing.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- Australian Government, energy.gov.au. Hot water systems — types, installation and energy performance
- Australian Building Codes Board. National Construction Code — Volume Three (Plumbing Code of Australia)