San Diego developing alternative water supplies

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.

San Diego's alternative water supplies

San Diego’s alternative water supplies

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.

The takeout

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.

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  1. Are they planning any conservation projects? I am curious to per capita use per person.

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    • I would also be interested in knowing if an increase in of solar energy use could be incorporated into these plans. This is not much of an article, and I live in Florida where I do not follow San Diego happenings, so I would hope my question is superfluous.

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  2. The macro distribution of water is a grid sort of thing. Rainwater catchment on roof tops is not. The embedded power is absent in rainwater. One can figure the manufacture footprint of the tank or a small amount of other cost, but If every building had a rainwater catchment as for hundreds of years in past, we would not need the infrastructure that is so embedded and decaying. Some in objection to this, claim the catchment of rooftop water would cause the rivers to dry up or the ground water to fall. Please, if this worries you, find out that facts show that is just not true in any measurable amount.
    My 15,000 gal tankage overflowed this year in a record drought. That is to say, it rained more than I could handle. So, I say, it is not the rain that is too little, it is my budget.

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    • Designing a rainwater harvesting system varies from country to country. In india, design of storage is made on the assumption that the max rainfall rate is not more than 1.25 inches per hour and does not exceed 6 inches in a 24 hour period. This is for collect, filter, store and use model. Use means for all purposes except drinking. In some places where the rain water is required to be used for potable purpose, water is subjected to UV Radiation which is said to kill 99.999 percent of bacteria and virus.
      If there is to be a rainfall water quantum exceeds storage available, the excess is diverted for recharge of groundwater through appropriate structures.
      Rivers can never go dry if roof top rainwater systems are installed to collect water from roof tops of buildings. The catchments cumulatively is only a small percentage of total catchment area of a river.

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    • How true you are! We seem to forget that less than a hundred years ago rainwater harvesting was common practice in rural communities, even at a time when rain was not an issue. Those people hadn’t even heard of climate change. Simply put it, they used to observe nature

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  3. Has ever been contemplated to develop the San Antonio Waste Water Plant into an energy and resources factory? Acting in that way the eventual energy consumption increase by reclamation can be more than offset by energy production from waste sludge conversion. A method developed and applied in the Netherlands, Germany and other European countries. This could be of advantage for San Diego as well demonstrating a viable and sustainable example of the circular economy of the water cycle.

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  4. I would also be interested in knowing if an increase in of solar energy use could be incorporated into these plans. This is not much of an article, and I live in Florida where I do not follow San Diego happenings, so I would hope my question is superfluous.

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  5. Certainly the need exists to develop alternative water supplies, especially on the west coast. As to climate change having any real impact upon availability of water, more and more scientists’ voices previously drowned out are now coming forward and disputing any actual Standard Methods related science behind this theory.

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  6. As soon as I noticed this site I went on reddit to share some of the love with them.

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    I am an environmentalist and only get involved in technologies which are pro planet. With other words use, promote and market products that will not do any harm to our environment and all life forms on our planet.
    WATER – only 3% of all water on our planet is ‘sweet’ water, of that about 70% are used for irrigation (to grow our food), more than 25% of these 3% are used in the various industries, a few percent are needed for our animals and what is left for us? Then where does the water fit in which is used on golf courses, parks, sport fields, gardens and landscaping?
    Climate Change is makeing things much worse not only in California but all around the world. How do we survive?
    Let us in this comment concentrate on the 70% used (wasted)in agriculture which does include the tunnel growers. What if we reduce this amount by at least 70 but mostly 80%? I am talking of a German technology – one of my babies – which does exactly that. It is ideal for tunnel growers, landscapers, gardeners, small holdings, sports fields, golf courses, farms. It is a one time investment – our longest running installations are now working for 20 years. It is an underground irrigation system that keeps the COMPLETE root area (no drippers)moist – no over watering, no evaporation, no power needed. Water recycling is important but this method is cheaper and just imagine the amount of water being saved!!!
    WE can deliver it to you ex Germany but much better would be to have production plants in the US to service all the draught stricken areas. The ROI for the plant itself is about a year.
    Anyone interested should get in contact with me.

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  8. Very good read. I am lucky to have located this forum after spending 2 hours surfing the web this evening. This is what I was looking for. Check out my codebooks over at if you get a chance.

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  9. San Diego needs to stop first wastage of water from household kitchen and bathroom basins where mandatory installation of sensor could be an option as an immediate measure. The water from these sources could be reused following standard technology options in place for purification. This will at least ensure huge drain of precious waters at a time the city is gravely afflicted with climate change induced drought.

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