Pool Evaporation Rate Chart: How Much Water Your Pool Loses & How to Reduce It

You top the pool up again, and it feels like you only did this last week. So is it a leak, or is it just evaporation doing what evaporation does? Most Australian pool owners underestimate this by a wide margin, mainly because nobody ever tells them how much water an average backyard pool actually holds, or how many litres of it disappear into the air on a hot, dry, windy day.

The real numbers are bigger than most people expect, and they compound. Every litre lost to evaporation takes dissolved chlorine, salt, and balancing chemicals with it, and every degree of heat that escapes with that water has to be paid for again the next time the heater kicks in. Over a full summer, an uncovered pool in a hot, dry capital can lose more water than its entire volume.

This guide sets out exactly how much water your pool loses to evaporation depending on where you live, shows you how to tell the difference between evaporation and a genuine leak, and explains the one change that stops almost all of it.

How Much Water Does Your Pool Actually Hold?

Before the evaporation numbers mean anything, it helps to know what you are actually working with. Most pool owners have never calculated their pool's true capacity, and the figure is usually larger than they assume.

Australian domestic swimming pools typically hold between 22,000 and 60,000 litres, with most sitting between 40,000 and 50,000 litres. Once you know your own pool's approximate capacity, the evaporation figures below become far easier to put into perspective, because losing a few hundred litres a day sounds trivial until you see it stacked against your pool's total volume across a season.

What Is Pool Water Evaporation and What Causes It?

Evaporation is simply the process of liquid water turning into vapour as its temperature rises relative to the surrounding air. It is the same process that empties a saucepan left boiling on the stove, just happening far more slowly and quietly across your entire pool surface, day and night.

Calculating an exact evaporation rate is genuinely complex, involving water temperature, air temperature, air pressure, humidity, and wind speed all interacting at once. For a backyard pool owner, the practical takeaway is simpler: evaporation never stops, it accelerates under specific conditions, and it is almost entirely preventable with the right cover.

What Factors Increase Evaporation Rates?

Four variables drive the vast majority of evaporation from an outdoor pool.

• Surface area. A larger pool has more exposed water, so it loses more litres per day at the same rate, even though the rate itself (measured in millimetres) stays the same.
• Temperature differential. The bigger the gap between water temperature and air temperature, the faster evaporation occurs. This is why a warm pool on a cool evening can lose a surprising amount of water overnight, even after the sun has gone down.
• Humidity. Dry air pulls moisture from the pool surface far more aggressively than humid air. This is a major reason Perth and Adelaide post higher evaporation rates than the more humid east coast cities, despite broadly comparable summer temperatures.
• Wind. This is the factor most pool owners underestimate. A gentle breeze strips away the thin layer of warm, moist air sitting just above the water surface, and can more than double the evaporation rate in the process. An exposed pool in a windy position loses dramatically more water than a sheltered one, all else being equal.

Pool Water Evaporation Chart by Australian City

Using long-term Bureau of Meteorology climate data for the six warmer months of the year (October to March, generally the core swimming season), the evaporation picture varies significantly by capital city.

Perth's combination of low humidity, strong sea breezes, and a long hot season pushes it to the top of the chart, well ahead of every other capital. Across the full six-month swimming season, that 9.2m x 4.5m Perth pool loses in the order of 62,000 litres to evaporation alone, more than the pool's entire capacity, and the losses do not stop once the weather cools. Evaporation continues year-round at a reduced rate, so even the two lowest-evaporation winter months still cost a Perth pool close to 3,000 litres each.

Every city on this chart shares the same underlying story: evaporation is a genuine, continuous, and measurable cost, and it is the single biggest source of water loss most outdoor pools experience.

How Much Water and Money Is Your Pool Losing Each Month?

It helps to translate these figures into something more tangible than millimetres and litres. A standard garden hose delivers somewhere in the order of 15 to 20 litres a minute, depending on local water pressure. Topping up a Perth pool losing 344 litres a day would mean running that hose for close to 20 minutes, every single day, just to stand still.

That water loss carries costs well beyond the tap. Every litre that evaporates takes its dissolved chlorine, stabiliser, and salt with it, meaning a pool losing water quickly also needs its chemicals replenished more often. Our guide to the importance of water chemistry breaks down exactly what happens when that balance drifts and what it costs to correct.

Heat loss compounds the problem for anyone running a heated pool. Water carries heat with it as it evaporates, so a pool losing hundreds of litres a day overnight is also losing a meaningful share of whatever the heater produced that day, forcing it to work harder to recover the same temperature each morning. Weighed against the cost of a quality cover, this ongoing combination of water, chemical, and heating losses usually tips the economics firmly in the cover's favour. Our guide to pool cover costs in Australia sets out pricing at every level of the market and how quickly a cover pays for itself.

Is It Evaporation or a Leak? How to Tell the Difference

Not every drop in water level is evaporation, and it is worth ruling out a genuine leak before assuming the numbers above explain everything you are seeing.

The clearest signs of a real leak, rather than ordinary evaporation, include water disappearing noticeably faster than the rates in the chart above, wet or soft patches appearing in the lawn or paving near the pool, a consistently rising water or sewer bill with no other explanation, and cracks or stains developing around the pool shell or fittings. Evaporation, by contrast, is steady, predictable, and closely tracks the weather. Days with strong wind and low humidity produce the biggest drops, and cooler, calmer, more humid days produce far less.

How Do You Perform a Bucket Test?

The bucket test remains the simplest, most reliable way to separate a leak from ordinary evaporation, and it takes only a few minutes to set up.

1. Fill a bucket with pool water to roughly the same level as the water in the pool.
2. Place the bucket on a step inside the pool, weighted down if needed so it does not float or tip.
3. Mark the water level in the bucket clearly with tape or a waterproof pen.
4. Leave it in place overnight, ideally for a full 24 hours, without swimming in the pool during that window.
5. Compare the two water levels the next day.

If the pool's water level has dropped noticeably more than the bucket's, that points to a leak somewhere in the shell, plumbing, or fittings, and it is worth calling in a professional to isolate the source. If both have dropped at roughly the same rate, evaporation is almost certainly the explanation, and the fix is far simpler than a leak repair.

How to Reduce Pool Water Evaporation

The single most effective step any Australian pool owner can take against evaporation is fitting a quality pool cover. Used consistently, a cover creates a physical barrier across the water surface, similar to putting a lid on a jar, and cuts evaporation by up to 97%.

That reduction flows through to every other cost this article has covered. Less water means less frequent chemical top-ups, and less overnight heat loss means less energy spent reheating the pool the next morning. Our detailed breakdown of why you need a pool cover covers the full water, chemical, and energy savings case in more depth.

The catch is that a cover only delivers these savings if it actually gets used, every night, without exception. This is where the choice of pool cover rollers matters as much as the cover itself. A cover that is awkward to handle ends up left off more nights than it is on, and every night it stays off, evaporation resumes at full rate.

Solar Covers vs Automated Covers vs Liquid Solar Blankets

Not every cover works the same way, and the right choice depends on how much manual effort you are prepared to put in and what else you want the cover to do.

Solar pool covers are the most common and cost-effective starting point. They float directly on the water surface, blocking evaporation while also transmitting solar energy into the pool during the day, giving a genuine heating benefit alongside the water savings.

Automated pool covers solve the consistency problem directly. A motorised, one-touch system removes the physical effort of deploying a wet cover every evening, which is usually the real reason a cover ends up sitting on the roller unused. For households that know a manual cover simply will not get used every night, an automated system is the more reliable long-term investment against evaporation.

Liquid solar blankets are worth mentioning for completeness, since some pool owners ask about them. These are chemical additives that form an invisible molecular layer on the water surface to slow evaporation. They can offer a modest reduction, but nowhere near the 97% figure a physical cover achieves, and the layer breaks down within weeks and needs regular reapplication.

If overnight heat retention through cooler months is the priority rather than daytime solar gain, thermal pool covers are purpose-built for that job, trading some of the solar heating benefit for stronger insulation. Whichever option suits your pool, look for products independently verified under the Smart Approved WaterMark scheme, which benchmarks genuine water efficiency claims rather than relying on manufacturer figures alone.

How Do Wind, Heat and Humidity Affect Evaporation?

The chart earlier in this guide uses long-term averages, but day-to-day evaporation can swing well above or below those figures depending on conditions.

Wind is the biggest single amplifier. Even a gentle breeze removes the thin layer of warm, moist air that naturally sits just above a pool's surface, and can more than double the evaporation rate compared with a still day. A pool in an exposed, open position loses substantially more water over a season than an equivalent pool sheltered by fencing, hedging, or nearby structures.

Temperature differential matters just as much, and it is not always the hottest day that produces the biggest loss. A pool that stays warm well after sunset, combined with a sharp drop in overnight air temperature, creates the largest gap between water and air temperature, and the largest evaporation spike, often overnight rather than during the heat of the day. This relationship between water temperature and evaporation is closely tied to the target temperature you run your pool at in the first place; our guide to ideal pool temperature in Australia explains how to balance comfort, chemistry, and running costs.

Humidity works in the opposite direction. The drier the surrounding air, the more aggressively it draws moisture from the pool surface, which is the main reason a hot, dry summer in Perth or Adelaide produces higher evaporation than an equally hot but more humid day in Brisbane or Sydney.

Why Elite Pool Covers Is the Right Partner for Reducing Water Loss

Cutting evaporation is not a one-size-fits-all decision, and the difference between an entry-level cover and a properly engineered one shows up every single day it is in use, compounding across its lifespan.

Elite Pool Covers has designed, manufactured, and supplied pool cover systems from Perth, Western Australia since 1989. Elite was the first Australian company to design, develop, and manufacture an automatic pool cover, the first to produce high-insulation solar blankets, and the first to manufacture an inground hideaway roller system. Elite was also selected to cover the pools for two World Swimming Championships held at Challenge Stadium in Western Australia, and has since supplied large-scale commercial cover and roller systems to facilities including HBF Stadium, Fiona Stanley Hospital, and Perth Children's Hospital.

Every pool cover in the Elite range, from entry-level solar blankets through to fully automated rigid slat systems, is manufactured to withstand harsh Australian UV, salt, and chemical conditions, and is backed by a pro-rata warranty from the Australian manufacturer behind it. Elite is a member of SPASA Australia, the peak industry body for the pool and spa sector, and supplies residential and commercial pools across Australia as well as export markets including New Zealand, South Africa, Spain, France, and the United Arab Emirates.

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