A system employing the classification DS3 is prescribed as a system of classification applying to relevant territorial waters, coastal waters and inland freshwaters.

The criterion for the classification DS3 is that the annual mean concentration of each substance listed in column (1) of the Schedule in samples taken and tested in accordance with these Regulations must not exceed the relevant concentration specified in column (2) of the Schedule.

The provisions of this regulation apply as respect the taking and testing of samples of any waters to which the classification DS3 is for the time being applied.

Samples must be taken in relation to such waters at a frequency sufficient to show any changes in the aquatic environment, having regard in particular to natural variations in hydrological conditions.

Where a discharge containing any substance listed in column (1) of the Schedule is made to such waters, samples must be taken at a point sufficiently close to the discharge point to be representative of the quality of the aquatic environment in the area affected by the discharge.

Samples taken in relation to such waters shall be analysed using the relevant reference methods of measurement specified in column (3) of the Schedule or other methods which have limits of detection, precision and accuracy at least as good.