Microbiological activity:

Microbiological activity is responsible for changes in the nitrate-nitrite ammonia balance for decrease in phenols and in BOD or for the reduction of sulphate to sulphide. Sulphite, ferrous iron, iodide and cyanide may be lost through oxidation. Color, odour and turbidity may increase, decrease or change quality. Sodium, silica and boron may be leached out of the glass container. Care should always be taken to obtain a sample that is truly representative of existing conditions and it should be handled in such a way that it does not deteriorate or become contaminated before reaching the laboratory. The record on the sample should include sufficient information to provide positive identification of the sample at a later date as well as the name of the sample collector, date, hour and exact location of collection. The water temperature, weather conditions, water level, stream flow also should preferably be indicated. Details of sampling points should be described by maps.

Before collecting samples from distribution system, the lines should be flushed for a sufficient period to ensure that the sample is representative of the supply, taking into account the diameter and length of the pipe to be flushed and the velocity of flow.