Officials in Orange County, Calif., will attend opening ceremonies today for the world's largest water-purification project, among the first "toilet-to-tap" systems in America. TheGroundwater Replenishment Systemis designed to take sewage water straight from bathrooms in places like Costa Mesa, Fullerton, and Newport Beach and-after an initial cleansing treatment-send it through $490 million worth of pipes, filters, and tanks for purification. The water then flows into lakes in nearby Anaheim, where it seeps through clay, sand, and rock into aquifers in the groundwater basin. Months later, it will travel back into the homes of half a million Orange County residents, through their kitchen taps and showerheads.

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