Swimming Pool Leak Test

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There is normal water loss from evaporation, splashing out and backwashing. A certain amount of topping up is desirable because it changes the water.

What is normal?

0.001 (1 millimetre) over 1 M2 = 1 litre

1,000 litres = 1 M3 (1 cubic metre)

0.002 per day should be considered the maximum average throughout the year and this equates to approx 24,000 litres for an 8 x 4 pool per year and 36,000 litres for a 10 x 5.
0.30 of rain in a year equates to 10,000 litres (15,000 litres).
A normal backwash consumes 25 - 50 litres and if this is done 50 times it amounts to 1,250 - 2,500 litres.
One backwash will reduce a pool by around 0.001.

Adding it all up you should be putting no more than 14,000 (26,00) litres

Most of the topping up should occur during the Summer and very little, if any, is required between November and March.

What causes the leaks (in approx order of frequency) -

Leaks from around Perforations in the Shell - the skimmer, return jets, underwater lights etc.

Plumbing Leaks - from the pipes or purification plant.

Shell Porosity - when the waterproof membrane allows water to pass.

Cracks in the Shell - due to structural faults.

Detecting Leaks

Important to remember - even if there are visible cracks, there may be other faults as well so it is important to test everything. The worst disaster is repairing a crack, cleaning, re-grouting and filling, only to find that there is a leak around the skimmer box as well.

1. Check for visible signs of plumbing leaks - Disconnect the waste pipe and run the filter. The multi-position control valve could need a new washer.

2. Set up the Equipment -

a) Place a wooden or metal batten across the corner of the pool and secure it with rocks so that it cannot move.
Make a mark in the centre - so that you are always measuring from the same point.

b) Cut down a square water bottle for the rain test, place it somewhere that it will catch the rain cleanly, mark one side with a felt-tip pen approx 0.50 up the side and fill it with water to this point.

3. First part of the test -

This is to check the integrity of the underground pipe-work. The test is not conclusive but it gives us a good idea.
If it rains during this test it is necessary to start over as we have to be extremely accurate.

a) Carefully mark the skimmer box around halfway and fill the pool exactly to this point.

b) Measure the distance from the batten to the water and note the time and measurement.

c) Run the filter continually for 20 - 30 hours.

d) Take the measurements again and make note. (Elapsed time and distance from the water to the batten.

e) Refill the pool exactly to the mark on the skimmer.

f) Repeat b), c) and d) but this time with the motor off and all control valves closed.

To take the measurement - slide the ruler slowly down the batten, keeping it as vertical as possible, and stop as soon as the ruler breaks the surface film. You will see that the water "jumps" up to the ruler.

Calculate the water loss (litres/hour) for the 2 tests as follows -

Millimetres x pool surface = litres. Divide by hours on test = litres/hour.

If the result is approx the same then there is no leak to worry about. If the 1st value is the greatest then there is probably a leak between the pump and the return jets. If the second is the greatest then it is between the bottom drain and the pump.

4. Second part of the test -

This is to test is there is leakage around the perforations to the shell (skimmer box, return jets etc.). If there is a visible crack than this part is really superfluous because, whilst the crack is being repaired and the pool is empty is is always best to re-point around these areas.

The test should be repeated every 3 - 7 days and continued until the water drops to below the lowest perforation.

a) Measure the distance from the water to the batten. Note down the measurement and the elapsed time.
Refill the water bottle to the mark each time and deduct for rainfall.
The motor should be off and everything closed down. The sanitizer level should be kept high (Chlorine 5 ppm, Bromine 3 ppm etc.) You won't be able to sweep the pool but you will be able to net out most of the debris.

b) Produce a chart showing the speed of water loss between different points.

You should now be able to see what is happening. There are endless possibilities but generally if the water stops at -

The bottom of the skimmer box then you have the most common fault of all - defective pointing around the box.

Just below the return jets then it is probably both of these.

Just below the lights then it is all three of them.

If it continues below the lights and you have registered a plumbing leak with the first part of the test then you have a leak in the pipe between the bottom drain and the pump. If you had no indication of a plumbing leak then it is the waterproof membrane.

Once the pool is empty all of the hidden pipe-work can be tested by a plumber carrying out a pressure test.