We can conserve our way out of California’s water problems.
Water conservation is important, but its effectiveness is often overstated.
Water conservation often targets reductions in diversions. However, not all water diverted is actually consumed. The left over water is often returned to the environment for reuse downstream. So, water use in a region is often much less than the sum of the individual diversions. Only a decrease in net water use saves water.
Reductions in water consumption are likely to arise from increases in the economic efficiency of irrigation (“more crop per drop”) combined with limiting irrigated land.
Subsurface drip irrigation is allowing San Joaquin Valley tomato growers to apply water precisely and uniformly, increasing yields and reducing the runoff of saline drainage.
Switching from thirsty lawns to drought tolerant plants can greatly reduce water consumed. However, reducing runoff from over watering only generates regional water savings if the excess water would not be recaptured in a stream or a groundwater basin.
Opportunities for water savings depend on location. Treated wastewater is often reused downstream. Thus reducing water diversions in Sacramento — where wastewater discharges are used downstream — has little effect on California’s net water use. Reducing water consumption in coastal areas — which discharge wastewater to the sea — produces substantial water savings.
Reducing diversions from streams and groundwater basins can yield environmental benefits, but diversions may not correspond to net water use.
Conservation is not a silver bullet; it should be combined with other water management approaches.