How Much Water Should Your Pool Lose? Understanding Normal Evaporation vs Pool Leaks
Updated July 2026 with current City of Cape Town water and sanitation tariffs.
Pool leaks account for a large share of the leak detection queries I get. Every week someone asks me the same question: "Werner, my pool is losing water. Is this normal, or do I have a leak?"
Evaporation is the biggest cause of normal water loss, and in Cape Town, with our warm dry summers and berg winds, it adds up quickly.
Normal Pool Water Loss: What to Expect
It is important to acknowledge that every pool loses water naturally. This is completely normal and happens through several processes:
Evaporation: Your Pool's Natural Process
Evaporation is by far the biggest culprit when it comes to normal water loss. Here in Cape Town, with our warm, dry summers and occasional berg winds, evaporation can be quite significant.
Typical evaporation rates:
- Summer: 6 to 12mm per day
- Winter: 2 to 5mm per day
- Windy days: can increase by 50 to 100%
For a standard 8m x 4m pool (32 square metres), that works out to:
- Summer: 190 to 380 litres per day
- Winter: 65 to 160 litres per day
That sounds alarming, and it is worth being straight with you: it is not free. Normal summer evaporation on a pool that size is around 6 to 11 kilolitres a month, which on current City tariffs costs somewhere between R540 and R1,130 a month on top of your household use. That is simply the cost of owning a pool in Cape Town. It is normal, it is unavoidable, and it is not what I am here to fix.
A leak is what comes on top of that.
Other Normal Water Loss
Beyond evaporation, you'll also lose water through:
- Splash-out during swimming: 50 to 200 litres per session
- Backwashing your filter: 300 to 1,000 litres depending on your system
- Regular maintenance and cleaning
The Simple Bucket Test
Here is the test I share with everyone who calls, because it costs nothing and it answers the question:
Place a bucket filled with pool water on your pool step, so it is partially submerged. Mark the water level in both the pool and the bucket. After 24 hours, compare them. If both have dropped by the same amount, you are looking at normal evaporation. If the pool has dropped significantly more than the bucket, you have a leak.
The bucket is exposed to the same sun and wind as the pool, so it evaporates at the same rate. Anything the pool loses beyond that is going somewhere else.
Why leaked water costs so much more than you expect
This is the part almost nobody understands, and it is the reason a pool leak can produce a genuinely shocking bill.
Cape Town charges water in steps. The more you use, the more each additional kilolitre costs. On current tariffs, a household using a normal amount pays around R55 per kilolitre. But once you go over 35 kilolitres in a month, every additional kilolitre jumps to R109.98.
Then there is the part that catches people out: sanitation is charged on the water your meter records, not on the water that reaches the sewer. So when your pool leaks into the ground, the City still bills you to treat it. Water and sanitation stack on top of each other.
Put those two things together and the water escaping from your pool is not costing you your average rate. It is costing you the top rate, roughly R110 for every 1,000 litres.
That is why the numbers get ugly so fast:
| Leak size | Costs you per day | Costs you per month |
| 500 litres a day | R52 | R1,550 |
| 1,000 litres a day | R108 | R3,250 |
| 1,500 litres a day | R163 | R4,900 |
| 3,000 litres a day | R328 | R9,850 |
| 10,000 litres a day | R1,098 | R32,940 |
Based on City of Cape Town 2026/27 domestic full, non-indigent tariffs including VAT, for a household with normal baseline usage. Tariffs are reviewed each July.
A leak most people would call small, losing a couple of thousand litres a day, is quietly costing more per month than most car repayments. And "small" really can be small: a hole no bigger than a pinhead, on a pressurised line, moves far more water over a day than anyone expects.
Video showing where the gas is pinpointing the leaking pool pipe
Video showing dye disappearing through a leaking inlet
Red flags that suggest a leak
- Water loss consistently over 12mm a day, even on calm days
- Constantly having to add chemicals
- Wet spots around the pool, especially near the equipment
- A cracked or settling pool deck
- Air bubbles in the return lines, which often points to a suction-side leak
- Algae despite correct chemical levels, because fresh water keeps diluting your chlorine
When to contact me
Get in touch if the bucket test shows the pool dropping faster than the bucket, if you are consistently losing more than 12mm a day, if you notice any of the red flags above, or if you suspect a leak but cannot find it.
I should be honest about something: not every pool that is losing water has a leak. In 6 of the roughly 86 reports I went through, there was no leak at all, and it could be confirmed. The loss turned out to be evaporation, backwashing, or splash-out, or in one case an automatic top-up system that had stuck and was quietly overfilling. That is a confirmed result, not a leak that could not be found, and it is a useful answer. It means you stop worrying, stop looking, and fix the actual cause.
What professional pool leak detection involves
I use a combination of methods, and which ones depend on what your pool is telling me:
- Trace gas, my most-used method on pools by a wide margin
- Fluorescent dye to confirm a suspected leak point
- Camera inspection to see inside the line once I know roughly where to look
- Pressure testing to isolate the return and suction loops independently
- Scuba inspection for a structural check where the pool needs it
Most pool leaks can be located and assessed within 2 to 3 hours. You get a written report with photographs showing exactly where the leak is, which you can hand to your pool company or submit with an insurance claim.
What it costs
Pool leak detection is a fixed price, which means no meter running and no surprises: you know what finding the leak costs before I arrive. That fixed price covers locating one leak. If I find a leak and it is repaired but the pool is still losing water, that points to a separate leak and is a separate job, because each one takes its own full round of testing to find. The fixed price covers the detection itself, not diving the pool, which is the one thing that falls outside it.
Fill in our online form with your address, a description of the water loss, and a photo or two of the pool and the pump setup, and I will tell you the price and what it covers. Please make sure your pool is topped up before I get there as I will need it full to perform all the tests.
The bottom line
Normal evaporation in Cape Town accounts for roughly 190 to 380 litres a day from a standard pool in summer. Anything consistently above that, especially when the weather does not explain it, is worth investigating.
Do the bucket test first. It is free and it takes a day. If the pool is losing more than the bucket, the water is going somewhere, and at R110 per thousand litres it is worth finding out where.
