How to Reduce Pool Evaporation: Litres by City and Month

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To reduce pool evaporation, cover the pool when it is not in use: SPASA puts the cut at 90–95%. Uncovered, an 8 × 4 m pool can lose up to 10,120 litres in a Perth January and 7,140–9,130 litres in the other four mainland capitals, on Bureau of Meteorology pan figures.

The short answer

The cover is the lever that matters. SPASA, the pool and spa industry association, says a cover cuts evaporation by 90–95% and saves about 3,000 litres a month.
Evaporation is seasonal, by a factor of two to five. On Bureau of Meteorology pan figures an 8 × 4 m pool loses up to 10,120 L in a Perth January and 2,080 L in July.
Perth’s pan rate is the highest of the five capitals we read, 5.7 mm a day averaged over the year; Melbourne Airport’s is the lowest, 4.7 mm.
Wind, water temperature and humidity drive the rest. SPASA says windbreaks can dramatically reduce evaporative loss, but publishes no percentage, so neither do we.
Pan figures are an upper bound. A small exposed pan evaporates faster than a larger, partly sheltered pool; rain also refills some of the loss.

Evaporation from an uncovered 8 × 4 m (32 m²) pool, worked from Bureau of Meteorology Class A pan mean daily evaporation (read 12 October 2026). Covered = SPASA’s 90–95% reduction. Upper bound: see the method note
City	BoM station and years	Pan mm/day, Jan / Jul	January, uncovered	January, covered	July, uncovered	Year, uncovered	Year, covered
Perth	Perth Airport (009021), 1981–2025	10.2 / 2.1	10,120 L	510–1,010 L	2,080 L	66.6 kL	3.3–6.7 kL
Adelaide	Adelaide Airport (023034), 1982–2024	9.2 / 2.0	9,130 L	460–910 L	1,980 L	61.9 kL	3.1–6.2 kL
Melbourne	Melbourne Airport (086282), 1998–2025	8.1 / 2.0	8,040 L	400–800 L	1,980 L	54.9 kL	2.7–5.5 kL
Sydney	Sydney Airport (066037), 1974–2026	7.3 / 2.7	7,240 L	360–720 L	2,680 L	58.4 kL	2.9–5.8 kL
Brisbane	Brisbane Aero (040842), 2000–2026	7.2 / 3.3	7,140 L	360–710 L	3,270 L	63.1 kL	3.2–6.3 kL

How much water is my pool losing to evaporation?

The method is one multiplication. One millimetre of water over one square metre is one litre, so litres lost = evaporation in mm a day × days × pool surface area in m². The Bureau of Meteorology publishes mean daily evaporation for each month, measured with a Class A evaporation pan, for each station with a pan.

Worked example, Perth in January. Perth Airport’s pan averages 10.2 mm a day in January (records 1981–2025). An 8 × 4 m pool has 32 m² of surface. 10.2 × 31 × 32 = 10,118 litres in the month. In July the pan averages 2.1 mm, which gives 2,083 litres. Over the year, 5.7 mm × 365 × 32 = 66,576 litres, about 66.6 kL.

Substitute your own pool’s area and your nearest station. Treat the answer as an upper bound: a small, exposed pan evaporates faster than a larger, partly sheltered pool, rain refills some of the loss, and backwashing and splash-out add some. The quotable line: an uncovered pool’s evaporation is a summer problem; a Perth pool loses nearly five times as much in January as in July.

How to reduce pool evaporation, lever by lever

Cover the pool whenever it is not in use. SPASA says a cover reduces evaporation by 90–95%. That figure assumes the cover is on; hours with the cover off lose part of the saving. Whether a cover is legally required is on do I need a pool cover, and its price and payback on pool cover cost and payback, so neither is repeated here.
Break the wind. SPASA says decreasing wind speed across the water can dramatically reduce evaporative loss, using fencing, screening or a line of evergreen planting, without shading the pool completely. It publishes no percentage, and we did not find one we could verify.
Do not heat the water more than you need. SPASA lists water temperature, air temperature, humidity and wind as the drivers of evaporation. A heated pool loses more water, and loses its heat with it; why your pool loses heat covers the surface heat budget.
Turn water features off when nobody is watching. Spray and falls add surface area and agitation. We found no published figure for how much.
Top up with rainwater. This does not cut evaporation, but SPASA suggests downpipe diverters or a tank so the top-up is not mains water.

If the water level keeps falling faster than these figures, or keeps falling with the cover on, it may be a leak, not evaporation; how to tell if your pool is leaking has the bucket test.

Which Australian city loses the most pool water to evaporation?

Of the five mainland capital stations we read, Perth Airport has the highest pan evaporation, 5.7 mm a day averaged over the year, which is 66.6 kL a year from an 8 × 4 m pool. Brisbane Aero is next at 5.4 mm, then Adelaide Airport at 5.3 mm, Sydney Airport at 5.0 mm and Melbourne Airport at 4.7 mm.

The seasonal swing is the more useful number for a pool owner. Brisbane’s pan rate only drops from 7.2 mm in January to 3.3 mm in July, so a Brisbane pool loses water all year. Perth, Adelaide and Melbourne fall from 8–10 mm in January to about 2 mm in July, so a cover earns most of its keep from November to March.

What that water costs depends on your water utility’s tariff, which is worked out for Sydney, Perth and Melbourne on what a pool adds to your water bill.

Designing a new pool to evaporate less

If the pool is not built yet, three design choices fix evaporation before it starts. A smaller surface area loses proportionally less, because the loss scales with square metres: a 6 × 3 m plunge pool has 18 m² against 32 m² for an 8 × 4 m pool, about 44% less. A sheltered position out of the prevailing wind helps, though full shade costs heat, as putting a pool in the shade explains. And a cover with a roller, built into the budget from day one, is used more than one bought later.

Ask for the cover, roller and any windbreak screening to be priced in the same quote as the pool, so you can compare like with like when you compare pool quotes.

Common questions

How much water does a pool lose to evaporation per day?

SPASA says an average backyard pool loses around 7mm a day in summer. Bureau of Meteorology pan figures for January range from 7.2 mm a day at Brisbane Aero to 10.2 mm at Perth Airport.

Does a pool cover stop evaporation?

It cuts it by 90–95% while it is on, according to SPASA, saving about 3,000 litres a month.

How do I calculate my pool’s evaporation?

Multiply the Bureau of Meteorology mean daily evaporation for your nearest station and month by the days in the month and your pool’s surface area in square metres. The answer is in litres.

Do windbreaks reduce pool evaporation?

Yes. SPASA says lowering wind speed across the water can dramatically reduce evaporation, using fencing, screens or evergreen planting. No verified percentage is published.

Is losing 5 mm a day normal for a pool?

In summer, often yes: January pan rates at the five capital stations are 7.2–10.2 mm a day. If the loss continues with the cover on, test for a leak.

Sources

General information only, current at 2026-10-12. Pool rules differ by state and by council, and penalty amounts are updated regularly. Confirm your own obligations with your council or a registered inspector before acting.