Why can't you swim in Hetch Hetchy?
Why can't you swim in Hetch Hetchy? Swimming and boating are prohibited in Hetch Hetchy Reservoir in order to maintain a clean source of drinking water. Public access is prohibited below the high-water mark of the reservoir. Pets are not allowed on the dam or on hiking trails.
Why is Hetch Hetchy water so good?
The water from Hetch Hetchy Reservoir is disinfected with chloramine (chlorine and ammonia) and UV light. San Francisco also gets water from other reservoirs and sometimes moves water from Hetch Hetchy to other reservoirs. This water is filtered - on average about 30% of the total supply.