A variety of measures are routinely monitored at customer taps to assess the bacteriological wholesomeness of the water. The number of samples with any coliforms present is considered a more general indicator of microbiological quality. Some coliforms naturally live in the distribution system while others arrive because the system integrity is compromised. Interestingly, the data showed no significant change in event frequency during 2003 (see Table ) but showed a large drop in 2004. Finally, plate counts provide a measure of the number of heterotrophic bacteria in the system. This bacterial class has no health significance, but some believe that in certain circumstances it indicates that the system may have been compromised. Analysing the frequency of samples with a positive count provides a general measure of their concentration. From Table it can be seen that plate-counts have more than halved since 2002. In contrast with bacteria coliforms, plate counts dropped immediately on the introduction of new treatment. In terms of public health, a balance has to be struck between having higher chlorine concentrations which produce more THMs plus a greater likelihood of taste and odour complaints, and ensuring the water is wholesome. Whilst there is desire to have a clear statement of where this optimum exists the reality is that the optimum varies both with the network and the water employed. What is clear is that reducing the organic load has had the benefit of reducing THMs and improving the wholesomeness of the water.