San Diego faces numerous challenges from climate change including increased temperatures resulting in more hotter and drier days, more prolonged heat waves, and more frequent droughts reducing availability of freshwater resources.
In addition to reduced water availability from climate change, San Diego is challenged by increasing demand for water – by 2035, the San Diego County Water Authority projects an increase in demand of 20% compared to average demand between 2005-2010 (after taking into account future water conservation, demand associated with long-term annexations and accelerated growth).
Currently, San Diego imports 85-90% of its water from the Colorado River and Northern California’s Bay Delta. However, with California stricken with drought and climate change increasing the probability of more intense and frequent droughts in the future San Diego does not have the option of simply increasing supply to meet increased demand.
To ensure security of supply, San Diego is developing alternative water supplies from potable reuse that will provide up to a third of the City’s water supply by 2035.
Developing alternative water supplies
The ‘Pure Water San Diego’ project will provide safe, reliable and cost-effective drinking water supplies for San Diego in addition to the recycled water the City already produces for agricultural and industrial use.
This 20-year project will involve the City’s North City Water Reclamation Plant pumping recycled water to the Advanced Water Purification Facility for membrane filtration, reverse osmosis, UV disinfection and advanced oxidation before the purified water is either:
- Stored in the City’s San Vicente Reservoir before blending with runoff and imported water from the Colorado River or the Bay Delta followed by treatment at the Drinking Water Treatment Plant that involves coagulation, filtration, disinfection, ozone and chlorine or,
- Directly pumped from the Advanced Water Purification Facility to the Drinking Water Treatment Plant before becoming potable water.
San Diego’s production of Pure Water is expected to increase energy consumption by the San Diego Public Utilities Department over and above current operations. However, because Pure Water will be replacing purchased imported water the whole project will be energy-neutral for the most part in terms of the difference in the embedded energy in an acre-foot (AF) of purified water with that of existing supplies.
According to the City’s 2013 Water Purification Demonstration Project, purified water produced at the City’s Reclamation Plant and pumped to the San Vicente reservoir would require approximately 2,500 kWh/AF compared to imported water requiring 2,000-3,300 kWh/AF of energy depending on the blend of water from the Colorado River or Bay-Delta.
Climate change is decreasing the availability of water in San Diego while demand is increasing so the City is exploring alternative water supplies; however, alternative supplies need to be energy-neutral as energy production is water-intensive.
*Robert C. Brears is the author of Urban Water Security (Wiley). Urban Water Security argues that, with climate change and rapid urbanization, cities need to transition from supply-side to demand-side management to achieve urban water security.