chapter  8
6 Pages

Foul drainage

Although metered consumption includes any water lost from the water supply system, the rate of infiltration of groundwater into the foul sewers can be estimated on average as being 10% of the flow in the sewer (new sewers) and 40% of the flow in the sewer (in the case of existing sewers) and this is approximately equal to the water lost from the water supply. As a result of this, when basing foul flows upon metered supplies, it is not generally necessary to make an allowance for infiltration unless a deduction is made for the waste from the metered water supply.