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A shallow pond where sunlight, bacterial action, and oxygen work to purify wastewater.

Lateral drain

Pipe serving an individual property that crosses into third party land, for example the public highway, to reach the public sewer.


Water that contains solute substances, so that it contains certain substances in solution after percolation through a filter or soil.


The process by which soluble materials in the soil, such as salts, nutrients, pesticide chemicals or contaminants, are washed into a lower layer of soil or are dissolved and carried away by water.


The water which leaks out of a water company's underground pipes or the private water supply pipes owned by customers.

Less sensitive areas

A water body or area where the discharge of wastewater does not adversely affect the environment. (See Annex II of EC directive 91/271/EEC). In the UK, also referred to as high natural dispersal areas (HNDAs).

Licence of appointment

Legal document granting water company permission to operate.


The quantity or mass of any substance transported in an effluent per unit time (the product of concentration of pollutant and effluent flow).

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