Aquatic weed control in storage reservoirs and conveyance systems of certain domestic water supply systems is a challenging problem to the waterworks engineer. The problem concerns not merely the control or elimination of aquatic growths. It involves water quality factors which may be inconsequential in other phases of aquatic weed control, but are of major importance in drinking water supplies. Where adequate treatment facilities are available, water quality factors are subject to control. However, many domestic water supply systems lack treatment facilities, and the effect on water quality by the use of any materials in the supply must be subjected to critical review.