Gross Microbiological Contamination

Posted by on Monday, April 25, 2016 Under: Pool Water Pollution
microbiological contamination in swimming pools

All commercial swimming pools should be getting the pool water tested at a UKAS-accredited laboratory for microbiological contamination. In most pools this should be done on a monthly frequency, but certain pools, such as hydrotherapy pools, should be done on a weekly basis. The four standard tests and the acceptable levels for each are:

  • Aerobic Colony Count  > 10cfu/ml
  • Total Coliforms  >10cfu/100ml 
  • E. Coli  >1cfu/100ml
  • Pseudomonas Aeruginosa  >50cfu/100ml 

If you get the lab results back and any of them are outside of these ranges, you need to get the water tested again as the samples may have been taken just after someone 'released' something into the water and the system has not had time to deal with it yet. If the repeat tests are still not within the acceptable ranges, the pool operator should take this as an indication that the pool water treatment and/or management system is not functioning as it should. The system and arrangements for managing the pool water quality will need to be looked at with a view to pinpointing exactly what is wrong and then putting it right. 
What if the results are way outside the acceptable ranges though? At what point does the pool operator need to close the pool down due to gross microbiological contamination? The official guidance is that the pool should be closed down if any of the routine monthly microbiological test results indicate either of the following scenarios:

  • Greater than 10 E.coli per 100ml in combination with an unsatisfactory aerobic colony count (>10 per 100ml) and/or an unsatisfactory P.aeruginosa count (>10 per 100ml) 
  • greater than 50 P.aeruginosa per 100ml in combination with a high aerobic colony count (>100 per ml) 
You may find it easier to interpret the above conditions by using the flow chart:
microbiological contamination in swimming pools flow chart

In : Pool Water Pollution