Mae Deddf 1975 yn ceisio sicrhau diogelwch y cyhoedd drwy osod rhwymedigaeth statudol ar ymgymerwyr cronfeydd dŵr uwchlaw cyfaint arbennig i dderbyn cyngor proffesiynol annibynnol a gweithredu arno ynghylch gallu’r gronfa ddŵr i reoli’r holl rymoedd a’r amodau a allai effeithio arni ac ymateb iddynt. Diben y rhwymedigaeth hon yw lleihau’r risgiau, hyd lefel dderbyniol, y gallai dŵr gael ei ryddhau mewn modd nad yw’n bosibl ei reoli, a allai beryglu bywydau pobl.
The 1975 Act seeks to ensure public safety through imposing a statutory obligation on the undertakers of reservoirs above a certain volume to take, and act on, independent professional advice on the integrity of the reservoir to manage and respond to all of the forces and conditions imposed on it. The purpose of this obligation is to reduce the risks of uncontrolled releases of water, which may lead to loss of life occurring, to an acceptable level.