Dear Mahshid Monitoring the ...

Dear Mahshid

Monitoring the microbiological quality of drinking water is conducted for two separate purposes. Firstly, a proper risk assessment must establish that water treatment is sufficient to manage the risk (World Health Organisation – Guidelines for Drinking Water Quality). It requires knowledge on the occurrence of waterborne pathogens (viruses, bacteria and protozoa) in the raw water and the ideal approach is to obtain this information from monitoring. If it is not feasible to do this, it is possible to make estimates based on the type of raw water.

The seconnd purpose is for routine monitoring to detect the presence of bacteria that indicate the potential presence of faecal contamination. Their occurrence may indicate a breach in the integrity of the water supply network that could potentially compromise public health. E. coli is just about still accepted as the universal indicator of faecal contamination. Controversy surrounds the significance of the other coliform bacteria, however. My view is that, whilst they are not necessarily definitive indicators of the presence of faecal contamination, they could still be indicating a potential pathway permitting ingress into the water supply.

You do not give your reasons for selecting the organisms you have listed or the monitoring regime. Testing for their presence would be no routine operational value. Their presence, however, is obviously very undesirable and would indicate a serious breach in the integrity of the network. Consequently, their origin would need to be sought and any deficiencies put right.