Microbiological Testing for Swimming Pools

If you own or manage a commercial pool, ensuring that the water is clean and safe for swimmers is crucial. Microbiological testing for swimming pools involves getting the water tested regularly at a UKAS-accredited laboratory for microbiological contamination.

Most pools should be tested monthly, but if you have a hydrotherapy pool, it’s recommended to get it tested weekly to maintain optimal hygiene levels.

When taking a microbiological sample, conducting a pool water chemical test simultaneously to measure free and combined chlorine levels and pH is important. Also, it’s essential to take note of water clarity and bather load to get a comprehensive overview of the pool’s condition.

Here are the tests you should know and their acceptable levels:


Aerobic Colony Count

This test measures the total number of bacteria that have formed a colony on the lab media under the test conditions. Acceptable levels should be under 10 colony-forming units per millilitre (cfu/ml).

Total Coliforms

Total coliforms include bacteria found in the soil, water affected by surface water, and human or animal waste. Faecal coliforms, a type of total coliform, are present in the faeces of warm-blooded animals. Therefore, high levels of total coliforms in pool water may indicate the presence of faecal or environmental contamination. Acceptable levels of total coliforms should be under 10 cfu per 100 millilitres (cfu/100ml).

E. coli

Escherichia coli, also known as E. coli, is a type of bacteria commonly found in the lower intestine of warm-blooded animals. Its presence in pool water indicates faecal contamination, and acceptable levels should be 0 cfu/100ml.

Pseudomonas Aeruginosa

These bacteria can cause skin infections and are commonly found in the environment. Their presence in pool water indicates that a part of the system, likely the filters, is colonised by the bacteria. Even without total coliforms, Pseudomonas aeruginosa can be present in a sample. Acceptable levels should be under 10 cfu/100ml.