Sampling by community water systems (CWS) is done at intervals during each month with the number of monthly samples based on the population served.
For non-community water systems (NCWS), the number of monthly samples also depends on whether the water source used is surface water (SW), ground water (GW) or ground water under the direct influence of surface water (GW-UDI). Under some conditions the State may reduce the sampling frequency to no less then 1 per year.
Unfiltered surface water systems and unfiltered ground water systems under the direct influence of surface water must analyze one coliform sample near the first service connection each day the source water exceeds the turbidity standard.
Repeat Sampling
If a routine sample is total coliform-positive, repeat sampling must be done within 24 hours of notification of a positive sample. Systems must take a certain number of repeat samples for each routine or repeat sample found to be total coliform-positive. The State may extend the 24-hour limit but may not waive this type of repeat sampling.
Small systems collecting fewer than five routine samples per month must collect five routine samples in the month following a total coliform-positive routine sample. Under some conditions the State may waive this type of repeat sampling.
The State may invalidate the results of some total coliform positive samples only if it determines the results are due to laboratory error or some other condition which does not reflect the actual water quality within the distribution system.
Return to Coliform Rule Page