Freshwater availability is the major constraint to agriculture in arid and semi-arid regions. The groundwater and energy conservation of applying reclaimed water for irrigation was analysed, using Southern California as the spatial domain for model testing. An extensive compilation of the most recent publicly available datasets was used to calculate the energy intensity for each water supply source, the associated carbon footprint reduction and the monetary savings associated with using reclaimed water over groundwater. Our results indicate that for 1998–2010 in California the fractional water use for agriculture is 0.81 and for urban use is 0.19. During this same period, an average of 4.2 × 1010 m3 of water were used for crop irrigation, of which 1%, 46.8% and 52.2% came from reclaimed water, groundwater, and surface water, respectively. Each of these three main water sources is associated with a range of energy intensity (in kWh m−3), depending on the process and environmental characteristics of the end-use location. Our analysis of multiple process and environmental configurations produced a detailed energy intensity database, with the associated carbon footprint. These databases are used to quantify the energy and carbon footprint difference between applying the current groundwater source and reclaimed water for irrigation.

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