The average rainfall over the 58 000 sq miles (150 000 km2) of England and Wales is 35-6 in (889 mm). About half is evaporated or transpired by vegetation and the remainder, representing some 41000m.g.d. (186 × 106m3/d) infiltrates the ground or becomes surface run-off. Under the terms of the Water Resources Act, 1963, the River Authorities have granted licences allowing an average abstraction of 24 000 million gallons of water each day (109 × 106m3/d). The principal demands for this water are indicated in Table 1.
The total includes 15 000 m.g.d. (68 × 106m3/d) required for cooling purposes, mainly by the Central Electricity Generating Board. This does not represent a measure of consumptive use; this total also includes some brackish water. If water for cooling is excluded, licences for ground water represent about 25 per cent of the total.
In south-east England (as defined in Anon 1966) the total licensed abstraction of 5500 m.g.d. (25 × 106m3/d) includes 3200 m.g.d. (14−5 × 106m3/d) used for cooling purposes of which 2600 m.g.d. (11−8 × 106m3/d) is brackish water from tidal stretches of rivers. Some 2900 m.g.d. (13−2 × 106m3/d) of the total is from inland waters representing about 44 per cent of the residual rainfall. If saline water for cooling purposes is excluded the quantities licensed from surface and ground water sources are 1500 and 1400 m.g.d. (6−8 × 106 and 6−4 × 106m3/d) respectively. The figures quoted above represent gross use; net use which takes into