Bacteriological Contaminants

Posted by on Saturday, December 17, 2011 Under: Pool Water Pollution
Every month, all public pools should be tested for bacteriological water quality by a UKAS accredited laboratory. These tests serve as a link of 'health check' and will give the pool operator an indication of the performance of the swimming pool plant system. There are four different tests that are carried out:

  • Aerobic colony count
  • Total coliforms
  • Escherichia coli
  • Pseudomonas aeruginosa

  • Aerobic Colony Count

    The first test, aerobic colony count, is a test for the number of bacteria in the sample of water which are capable of forming colonies of visible bacteria, when it has been incubated at 37 degrees Celsius (ie, normal human body temperature) for 24 hours. The test doesn't necessarily differentiate between different types of bacteria, but looks at the overall picture and will provide the pool operator with an overview of the efficiency of the pool plant system. The test is expressed as the number of visible colony forming units (cfu's) counted in a sample of one ml of pool water and there should be less than 10 of these present after 24 hours at 37 degrees C in a well managed pool. If you get a result of more than 10 cfu's don't immediately assume that there is a major problem. Remember - the aerobic colony count is a measure of ALL bacteria capable of forming visible colonies. Further tests would need to be carried out in order to get more information about what types of bacteria we are dealing with.

    This is where the testing begins to provide more specific information. Coliforms are a type of bacteria that are present in (amongst other places) the faeces of warm-blooded mammals. Coliforms on there own are not normally the cause of serious illness, but since they cannot multiply in pool water, if you get any showing up in your results, it is very likely that they have been introduced into the pool via faecal matter (or possibly environmental contamination as they are also found on plant and soil). This means that there could well be other types of pathogenic (ie, harmful) bacteria present also. 
    You should be getting less than 10 cfu's per 100ml sample of pool water in a well run swimming pool. If your getting results over and above this, along with high results on the aerobic colony count test, it's likely that either the sample was taken shortly after a faecal contamination, or there may be problems with the pool plant system. Another test will need to be carried out to confirm.

    Escherichia coli 
    E. Coli is are present in the intestines of humans and many strains or non-pathogenic (ie, not harmful). Some strains are pathogenic though and can cause serious illness. If your getting any showing up in your results, then there is little doubt that it got there via faecal contamination. Coloforms and E. Coli are both killed by chlorine, so you should not be getting any more than 10 cfu's in a well-run pool, but similar to above, the sample could have been taken shortly after a faecal contamination. The result needs to be considered alongside all the other results in order to build a picture of what's happening with the water. If repeat tests still show high results, take it as a red flag; something's not right somewhere.

    Pseudomonas Aeruginosa
    Pseudomonas bacteria are present in in the environment, and on humans, and are capable of growing in water. They can cause ear and skin infections, but are killed by chlorine, so as long as you keep your disinfection levels within the recommended parameters, there should be no issues and you should not see results above 10 cfu's per 100ml in a well-run pool. If your getting any showing up in repeat samples, then it is looking probable that they have colonised the filters, or some other area of the circulation system, probably due to poor disinfection and/or filtration.

    The ideal result with all these tests is to have zero across the board. If your getting some results that indicate the presence of any of the above, you need to look further and consider all of the results together, as they are quite closely linked. If your results indicate gross contamination, you will need to close the pool and get to the bottom of the problem. Please see below (click to enlarge) for a simple flow chart, which will help you to interpret the results and determine whether you have gross contamination of your pool water:  

    In : Pool Water Pollution 

    Tags: "cfu's - colony forming units" "microbiological testing" "bacteriological testing" "e coli" "aerobic colony count" "total coliforms" "bacteria" "pseudomonas aeruginosa" "ukas"