Local governments in Perth, Western Australia, use groundwater to irrigate high value public open space. Due to a sustained decline in rainfall current groundwater extraction rates are unsustainable and are set to be reduced. We investigate the cost-effectiveness of different water efficiency improvement technology solutions. There is significant variation in the cost-effectiveness of different techniques, with the cost of water saved varying from a low of AUD 0.27 per kilolitre to as high as AUD 13.49 per kilolitre. In most cases the water efficiency solutions considered delivered water savings for less than the cost of the backstop technique – scheme water – which costs AUD 2.09 per kilolitre. For the case study area we find that 5, 10, and 15% saving in the volume of water used to irrigate public open space can be achieved for average per kilolitre water costs of: AUD 0.38, AUD 0.43, and AUD 0.62, respectively.