Evaporative cooling water usage is one of the more common questions Evaporative Air Conditioning Perth homeowners ask once they’ve had a system running for a season or two, especially when a water bill lands and they want to know how much of it is actually down to the cooler. It’s a fair question, since evaporative systems rely on water to cool incoming air, unlike refrigerated systems that don’t use water at all.
This guide breaks down how much water an evaporative cooling system typically uses, from litres per hour through to a full Perth summer, along with what actually drives that usage up or down.
How Many Litres Per Hour Does Evaporative Cooling Use?
A typical residential evaporative cooling system uses somewhere around 10 to 15 litres of water per hour, depending on the size of the unit and how many outlets it’s feeding. Larger ducted systems covering bigger homes can use up to 20 litres per hour or more on high fan speed.
This figure covers the water absorbed by the cooling pads as well as a portion used in periodic bleed-off, which we’ll get to shortly.
How Much Water Does It Use Per Day?
Running a typical system for around 8 hours a day generally works out to somewhere between 80 and 160 litres of water use per day. On longer days, or with the system running for 12 to 16 hours during a heatwave, that can climb to roughly 120 to 320 litres.
The exact figure depends heavily on fan speed, outdoor temperature, and how many hours the system is actually running rather than just switched on.
How Much Water Does It Use Over Summer?
Across a Perth summer, running the system for around 8 hours a day on most warm days typically adds up to somewhere between 7,000 and 14,000 litres over December, January and February combined. Households running the system longer each day, or through more of the hotter stretches, will sit toward the higher end of that range.
For context, that’s a modest amount compared with general household water use over the same period, but it’s still worth factoring in when budgeting for summer running costs.
Does Fan Speed Change Water Consumption?
Yes. Running on a higher fan speed increases water consumption, since more air is being pulled through the cooling pads, which need more water to stay properly saturated. Lower or medium fan speeds generally use noticeably less water for a comparable level of cooling, particularly if the system is left running steadily rather than cycled on high in short bursts.
Does Weather Affect Water Usage?
Yes, weather plays a significant role. On hot, dry days, more water evaporates from the cooling pads to cool the air moving through, which increases consumption. On milder or more humid days, less water evaporates, so usage drops off naturally.
This is part of why evaporative cooling water usage isn’t a fixed number. It moves with the weather in a fairly direct way, unlike a refrigerated system’s water use, which stays at zero regardless of conditions.
Does the System Constantly Use Water?
Not constantly in the sense of a continuous flow, but water is being drawn on the whole time the system is running. The pump keeps the cooling pads wet, water evaporates as air passes through, and the system tops up the tray to maintain the right water level throughout operation.
On top of that, most systems also periodically drain and refill a portion of the water tray, which adds to overall consumption beyond just what evaporates through the pads.
Why Does an Evaporative Cooler Dump Water?
Evaporative coolers periodically drain, or “bleed off,” a portion of the water in the tray and replace it with fresh water. This happens because as water evaporates from the pads, minerals and salts in the water stay behind and gradually concentrate in the tray.
Without this bleed-off process, mineral concentration would build up, leading to scale on the pads and components, reduced cooling performance, and a shorter lifespan for the pads. It’s a normal and necessary part of how the system operates, not a fault or a leak.
Does an Old Cooler Use More Water?
Generally, yes. As a system ages, worn seals, a less efficient pump, or scale build-up in the tray and on the pads can all lead to less efficient water use. In some cases, ageing components can cause water to overflow, leak, or bleed off more often than necessary, pushing consumption higher than it should be.
A well-maintained system, regardless of age, will generally use water more efficiently than one that’s overdue for a service.
How Much Does the Water Cost?
Water is a relatively small part of the overall running cost. At standard Perth water rates, evaporative cooling water use typically adds up to just a few cents per hour, or roughly $2 to $5 a month for a household running the system regularly through summer.
Across a full Perth summer, total water cost generally lands somewhere between $15 and $35, which is minor compared with the electricity cost of running the system. For a broader breakdown of running costs, see our guide on evaporative cooling running costs in Perth.
How Can I Reduce Water Usage?
A few practical ways to keep water usage down include:
- Running the system on a lower or medium fan speed where possible
- Keeping cooling pads clean, since worn or scaled pads can waste water through uneven saturation
- Booking regular servicing to catch pump issues, leaks, or float valve faults early
- Using a timer or thermostat control so the system isn’t running longer than needed
- Checking for visible leaks around the tray, pump, or water line connections
Most of these overlap with good general maintenance, since a system that’s running efficiently also tends to use water more efficiently.
Is Evaporative Cooling Still Economical After Water Costs?
Yes. Even accounting for water use, evaporative cooling remains considerably cheaper to run than a comparable ducted reverse cycle system, mainly because water costs are a small fraction of the overall running cost compared with electricity. The bulk of the cost still comes down to power consumption from the fan and pump, not water.
Factoring in both electricity and water, evaporative cooling generally stays one of the more cost-effective ways to cool a Perth home through summer, particularly in the dry conditions the system is designed for.
Keep Water Usage in Check With Regular Servicing
Water usage naturally varies with weather, fan speed, and system size, but an ageing or poorly maintained unit will almost always use more than it needs to. Regular servicing keeps the pump, pads, and tray working efficiently, which keeps both water and electricity costs under control.
Get in touch with our team or call 1300 164 217 if you’d like your system checked, or find out more on our evaporative air conditioning page.
