Question

There are currently 170,000 or more chemicals which must be monitored by your town's water treatment plant. How do you think decisions are made as to how often a given material is tested ?

Answer 1

In the quality control and assurance of water treatment plants, engineers and chemists must watch closely the general environmental conditions of the catchment and distribution of drinking water and make statisticals tests to estimate the concentration's changes of some substances that can be harmful for the people and industries consumption.

By making comprehensive sampling of soils, air, liquid tributaries and industrial effluents near to the water sources, and having the ability to change randomly the location of sampling points, an idea of the incidence of environment upon the source can be raised in the staff in charge of monitoring water compositions.

Once that water has be consumed by people, the epidemiological surveillance of several patologies transmitted by water is an useful tool to establish decisions to correct the generated problems.

The frequency of the material testing will depend on the total population under the influence of the consumption of that public service. A major population requires a stricter control from the sanitaries authorities

If we have a water treatment plant of wastewater or industrial waters, the frequency of testing must be much more periodic due to the large quantities of pollutants in the household and industrial sewages.

Obviously, it is not possible to run 170,000 analysis in water samples. Most of them are exceptionally rare to find in mensurable quantities, and hence, are not monitored with a capital importance. In practice, only a few tens of those chemicals are monitored with a regular frequency: daily, weekly, monthly or yearly.