UV is certainly easier to deploy than chlorine gas (a UV leak won't poison everyone in the room via gas inhalation), but it's still dangerous at the scales used

UV is certainly easier to deploy than chlorine gas (a UV leak won't poison everyone in the room via gas inhalation), but it's still dangerous at the scales used to sterilize large quantities of water. The bigger problem than either is that AFAIK, few places bother to sterilize their effluent. I'm not even sure if San Francisco bothers to do that, actually...