Swimming Pool Balance Tanks

Within a pool facility there are many potential uses of water where users and those in the vicinity may be exposed to hazards with the potential to cause injury and waterborne illness.

In general, the importance of a balance between public health demands and consumer acceptability are similar for both drinking and swimming waters. Disinfection cannot be compromised but can be aimed towards minimising both disinfectant levels and the formation of unwanted substances, including disinfection by-products.

Along with filtration and chemical dosing, balance tank cleaning is key to keeping the pool water well balanced and safe.

Balance tank cleaning, is recommended by PWTAG (Pool Water Treatment Advisory Group). Balance tanks should be inspected at least once a year and cleaned as necessary. Debris should be removed and inner surfaces brushed and flushed down with 10mg/l chlorinated water, which can be returned to the circulation system via the filters.

The swimming pool balance tank is an important but often forgotten feature in the pool filtration system that plays a significant role in maintaining a constant water level in deck level and spa pools. It is situated in between the filtration system and the pool tank itself, providing an intermediate to hold the water displaced by bathers entering the pool before releasing the water back into the tank as bathers leave to give a constant water level.

Due to its positioning before the filtration system and the constant transfer of water within the pool, the balance tank accumulates a large amount of debris and contaminants. This provides a prime breeding ground for a variety of bacteria, particularly on the walls of the tank as the water level rises and falls. If not cleaned regularly can pose a serious threat to pool hygiene.

WES are able to provide the full inspection and clean of balance tanks recommended by the PWTAG Code of Practice, including debris removal, clean and disinfection of all surfaces, inspection of valves and pipework, whilst adhering to HSE standards for working within a confined space.

If it has been longer than a year since your balance tank was last inspected and cleaned contact us now to ensure the hygiene and satisfaction of your customers!

Microbiological Testing

Frequency and protocol

Tests should be performed monthly to monitor the presence of microorganisms. Tests should also be done:

  • before a pool is used for the first time
  • before it is put back into use, after having been shut down for repairs
  • if there are difficulties with the treatment system
  • if contamination has been noted
  • as part of any investigation into possible adverse effects on bathers’ health.

More frequent sampling will be necessary if there is a problem or for particularly heavily loaded pools. Hydrotherapy pools, even those not in a healthcare setting, should be tested weekly. Microbiological testing should be performed only by competent and accredited personnel at a UKAS laboratory. Samples should be taken as in 11.3.3 (PWTAG) and in accordance with BS EN ISO 19458:2006. Whenever a microbiological sample is taken it is important that a pool water chemical test of free and combined chlorine and pH is taken at the same time as a reference.

Routine Monthly Water Analysis

Total Viable Count

TVC is an overall indicator of the bacteriological water quality, in themselves they do not indicate that the water is harmful, high numbers can indicate that the filtration/disinfection system should be investigated.

Total coliforms

Bacteria, universally present in the faeces of mammals, of which E coli is an example.

E coli

A bacterium in human or animal faeces – one of the coliform organisms routinely monitored for signs of faecal pollution.

Pseudomonas aeruginosa

The Pseudomonas group are widespread in nature occurring commonly in water and soil and on damp or moist surfaces. When these organisms are present they may proliferate utilising nutrients either from the water or from plumbing materials used in the distribution system

Additional Water Analysis


If faecal contamination has only been reported and there is some doubt about the accuracy of the report, its presence should be confirmed as a matter of urgency.

Solid faeces: the stools should immediately be removed from the pool using a scoop or fine mesh net and flushed down the toilet (not put in any pool drains). Then if there is any doubt that all the faeces have been captured and disposed of, and there is possible widespread distribution of the faeces in the pool, then the pool should be closed immediately.

Runny faeces: assume that the diarrhoea is caused by Cryptosporidium, a chlorine-resistant protozoan; then this is the code to follow. (Operators may well not know if this organism is involved, in which case this is the safest option.) Close the pool – and any other pools whose water treatment is linked to the fouled pool. If people transfer to another pool, perhaps from a teaching pool to a main or leisure pool, they should shower first.

Sample Results

The total viable count (colony count) should not be more than 10 colony forming units (cfu) per mill litre of pool water at 37°C for 24h.

A colony count in excess of 100 cfu/ml is unsatisfactory.

A consistently raised colony count of 10 to100 cfu/ml is unsatisfactory and should be investigated.

Total coliforms should be absent in 100ml. Less than 10 per 100ml is acceptable provided it does not happen in consecutive samples, there are no Escheria coli, the colony count is less than 10 cfu/ml and the residual disinfectant concentration and pH values are within the recommended ranges.

E coli should be absent in a 100ml sample.

Pseudomonas aeruginosa should be absent in a 100ml sample. If the count is over 10 cfu/100 ml, the test should be repeated.

Where repeated samples contain P aeruginosa, the filtration and disinfection procedures should be examined to determine whether there are areas within the pool circulation where the organism is able to multiply. When counts exceed 50 cfu/100 ml pool closure is advised.

Acting on failures/pool closure

If a result is unsatisfactory, a preliminary investigation should be undertaken and the test should be repeated as soon as practicably possible.

If the second result is also unsatisfactory, the pool’s management and operation should be investigated and the test repeated.

If the third result is still unsatisfactory, immediate remedial action is required, which may mean closing the pool.

The pool should be closed if there is chemical or physical evidence of unsatisfactory disinfection.

The pool should be closed if microbiological testing discloses gross contamination, which means one of two things:

E coli over 10 per 100 ml PLUS either colony count over 10 cfu per ml or P aeruginosa over 10 per 100 ml (or, of course, both).

P aeruginosa over 50 per 100 ml PLUS colony count over 100 per ml.