The reservoir now supplies water to the towns in the valley of the River Tawe and north Swansea.

The reservoir is one of several established in what is now the Brecon Beacons National Park, an area of Old Red Sandstone peaks with relatively high rainfall.

[1] The 28-metre high dam is within a wide glaciated valley and is estimated to impound some 1,007,000,000 gallons of water.

Upstream of Crai Reservoir the land is largely upland moorlands or unimproved grassland with one area now given over to coniferous forestry.

The treatment of screening, disinfection and lime dosing is carried out south of the reservoir at Nant yr Wydd.