Eilene Zimmerman describes the world's largest water purification project in Orange COunty, California, "The Groundwater Replenishment System is 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."
But such "toilet to tap" systems apparently face resistance from a "public (that) hasn't yet warmed to the notion of indirect potable reuse (IPR)". Despite most of our major waterbodies, source for most of our drinking water, being heavily polluted, people still find it repulsive to use treated sewerage water. But given the spectre of "water wars" it may not be too far ahead in time when such water becomes perfectly acceptable.