B4.2 Definitions relating to Water


Between 70% and 75% of the earth’s surface is covered with water.


Controlled Waters

Controlled Waters are defined in Section 30A of the Control of Pollution Act 1974 and in Section 104 of the Water Resources Act 1991, as:

  • Relevant territorial waters – the waters which extend seaward for three miles.
  • Coastal waters – any waters which are within the area which extends landward from those baselines as far as:
    • the limit of the highest tide
    • in the case of the waters of a river – the fresh-water limit of the river or watercourse together with the waters of any enclosed dock which adjoins waters within that area
  • Inland freshwaters – the waters of any relevant lake or pond or of so much of any relevant river or watercourse as is above the fresh-water limit.
  • Ground waters – any waters contained in underground strata.


In Scotland, Section 3 of the Contaminated Land (Scotland) Regulations 2005 [SI no. 658] have replaced the term Controlled Waters with “water environment”.


A watercourse is defined in the Land Drainage Act 1991 as including “all rivers and streams and all ditches drains, cuts, culverts, dikes, sewers (other than public sewers within the meaning of the Water Industry Act 1991) and passages, through which water flows”.

The Act does not state that water must flow through the watercourse at all times to be a watercourse.

Main River:

Main rivers are usually larger streams and rivers. However, they do include smaller watercourses of local significance. A main river is a watercourse marked as such on a main river map, as determined by DEFRA (Department of Environment, Food & Rural Affairs). This is an official document.

Ordinary Watercourse:

An ordinary watercourse is every river, stream, ditch, drain, cut, dyke, sluice, sewer (other than a public sewer) and passage through which water flows and which does not form part of a main river.

The Local Authority, or Internal Drainage Board where relevant, has powers for ordinary watercourses that are similar to those that the Environment Agency has for main rivers.