Engineering360: "World's largest water recycling facility now complete"

Looks expensive. I could see doing that if you were going to pipe it right back to the municipal water supply. Since it is being dumped into basins to percolate back into the soil, why do any more treatment than you would do before dumping it into the ocean?

Residential septic systems percolate barely treated effluent back into the soil. Mother Nature takes care of the rest of the treatment to make it safe enough to drink again after passing through more than 100 feet of soil (minimum distance from drain fields to drinking wells, plus the depth of the well).