4.2.4—Increasing water supplies

Choose a supply option by the water problem it solves and the cost or impact it introduces.

Reservoirs shift water through time but alter rivers; rain capture depends on rainfall and storage; reverse-osmosis desalination forces water through a semi-permeable membrane, adding coastal supply but using energy and producing concentrated brine; enhanced wetlands store and filter water while supporting habitat.

A coastal city with drought but reliable power may consider desalination, while an inland wet-season city may gain more from storage and rain capture.

Rainwater harvesting becomes unreliable during long dry periods or when storage is too small, so supply reliability must be matched to demand timing.

‘New supply’ is not impact-free water; include energy, ecology, quality and social costs.