At the San Francisco Public Utilities Commission building the water they drink may some come from rain water collected on the roof but also from office toilets and sinks. That water is first heavily filtered as part of a wastewater filtration test, and representatives of the PUC say it tastes just as good as potable tap water.
The wastewater is put through what is described as the building wetlands system of gravel, soil, and plants. It is then a filtration system, reverse osmosis, and exposed to UV light to kill and remaining bacteria.
The recycled water is tested for safety before people take a drink, and it's been stripped down so much that minerals would have to be added before it could be mixed into the city water system.
This wastewater reclamation project is part of San Francisco's effort to prepare for anticipated state legislation mandating that wastewater be turned into drinking water come 2023. Before that time, city officials plan to share data on this project with their counterparts in other cities who have an interest in purifying water running down our drains and flowing through our sewer systems.