Frequency of Sampling:

The frequency of collection of samples normally depends on the variability of the quality of tested water, the types of treatment processes used and other local factors. Samples for general systematic chemical examination should be collected at least once every three months in supplies serving more than 50,000 populations and at least twice a year on supplies upto 50,000 populations. However, more frequent sampling may be needed as per the local conditions.

For bacteriological sampling, the frequency of sampling and the locations of the sampling points should be such as to enable proper evaluation of bacteriological quality of entire water supply. The recommended number of samples to be collected from water distribution system is given in Table.

Table: Minimum Sampling Frequency and Number from Distribution System