A number of sites in the distribution system are required to be sampled for water quality parameters, dependent on population served by the water supply and whether the supply is on standard or reduced monitoring.
| Supply size (# of people served) | Number of sites (standard monitoring) | Number of sites (reduced monitoring) |
|---|---|---|
| More than 100,000 | 25 | 10 |
| 10,001 - 100,000 | 10 | 7 |
| 3,301 - 10,000 | 3 | 3 |
| 501 - 3,300 | 2 | 2 |
| 101 - 500 | 1 | 1 |
| Fewer than 101 | 1 | 1 |
Typically, the collection frequency of these distribution samples is quarterly, however a water supply should refer to its annual monitoring schedule for the required number of samples to be collected, the sample collection frequency, and the water quality parameters to be analyzed.
The distribution sampling sites must be representative of the distribution system, taking into consideration the number of persons served, and the different sources of water and treatment types utilized by the supply. Samples may be collected at residential or non-residential locations. It is recommended to consider using designated bacteriological sampling locations as water quality parameter sample sites.
Each round of sampling should ideally be conducted at the same sampling sites. Samples may not be taken from taps that have point-of-use or point-of-entry treatment devices, such as a reverse osmosis system or water softener. It is recommended to run each tap for 5 to 10 minutes before collecting the samples.
Certain water quality parameter samples should be measured with a field kit, while other samples may be submitted to a laboratory for analysis. A water supply must ensure that field test instruments are calibrated and maintained according to manufacturer specifications. When submitting samples to a laboratory, a water supply should ensure that the required hold times, thermal preservation, and other requirements are met.
