The Waiau scheme is the largest scheme for AIC and was completed in 1978. It takes 11 cubic metres per second of water from the Waiau River at the Leslie Hills Road Bridge, which is then gravity fed along open races towards farmland closer to the townships of Culverden and Rotherham.

The scheme was originally set up for borderdyke irrigation which meant a standard unit flow of 0.35 cubic metres per second was provided to each property once every 17 days during the irrigation season. Now 99% of irrigation within this scheme is by spray irrigation.