Yesterday the San Diego Union Tribune ran a feature Future wellspring? - New source of drinking water hinges on pilot project and City Council.
The article contains a great graphic showing the multiple levels of treatment that would be included in the project.
The process starts with wastewater that has already has been treated to levels deemed acceptable for use on landscaping. Then it’s pumped through a microfiltration process that removes bacteria, protozoa and suspended particles. The water then is them pumped reverse osmosis membranes to remove dissolved impurities. Finally, the twice-filtered water is exposed to UV light and hydrogen peroxide in a process known as "advanced oxidation." The pilot plant that will produce about 1 million gallons per day is expected to be in operation by April.
This is essentially the same process being used in Orange County to produce 70 million gallons per day of high quality drinking water - and reduce wastewater discharges to the ocean.