Hetch Hetchy Reservoir

Protected Reservoir · West

Serves 8 cities in our database · ~2,240,470 residents

116
Avg Hardness (PPM)
1.1
Avg PFAS (ppt)
4.1
Avg Lead (ppb)
8
Cities Served
Soft
0Slightly
60Moderate
120Hard
180Very Hard
250Extreme
400+
116 PPM Moderately Hard
CONTAMINANT LEVELS Hardness 116 PPM TDS 205 PPM PFAS 1.1 ppt Lead 4.1 ppb Chlorine 1.2 mg/L Nitrate 1.8 mg/L

About Hetch Hetchy Reservoir

San Francisco drinks glacier-fed water from Hetch Hetchy Reservoir in Yosemite National Park. Like Portland, the water is so clean it is exempt from federal filtration requirements.

Geography & Hydrology

The reservoir sits at 3,783 feet elevation in Yosemite. Water travels 167 miles by gravity through tunnels and pipelines to the Bay Area. The O'Shaughnessy Dam, completed in 1923, created the reservoir in a valley John Muir called a second Yosemite.

How Hetch Hetchy Reservoir Water Is Treated

UV disinfection, chloramine, and fluoride. No filtration required — one of only a handful of surface water systems in the US with this exemption. The granite watershed produces extremely soft, low-mineral water.

Across the 8 cities we track, water from Hetch Hetchy Reservoir averages 116 PPM hardness (Moderately Hard), ranging from 21 to 214 PPM. This is relatively soft water - a water softener is generally not needed.

Current Challenges

Climate change reducing Sierra snowpack, wildfire risk to the watershed, aging infrastructure (100-year-old tunnels), and political pressure to remove the dam and restore the Hetch Hetchy Valley.

Cities Supplied by Hetch Hetchy Reservoir

Water quality varies by city due to local treatment, distribution infrastructure, and source blending.

San Jose, CA

183 PPM · Very Hard 1,039,920 residents

Fremont, CA

192 PPM · Very Hard 344,000 residents

Newark, CA

90 PPM · Moderately Hard 344,000 residents

Hayward, CA

214 PPM · Very Hard 162,954 residents

Daly City, CA

34 PPM · Slightly Hard 104,901 residents

Dublin, CA

60 PPM · Moderately Hard 98,776 residents

Milpitas, CA

130 PPM · Hard 81,773 residents

San Francisco, CA

21 PPM · Slightly Hard 64,146 residents

Recommended for Hetch Hetchy Reservoir Water

Based on average water quality across 8 cities supplied by Hetch Hetchy Reservoir.

Test Your Tap Home Water Test Kit ~$30

Affiliate disclosure: we may earn a commission on purchases. Recommendations based on water quality data.

Frequently Asked Questions

Is Hetch Hetchy Reservoir water safe to drink?
Water from Hetch Hetchy Reservoir meets EPA safety standards in all served cities. Contaminant levels are within legal limits, though additional filtration can improve quality beyond legal minimums.
Why is Hetch Hetchy Reservoir water soft?
Hetch Hetchy Reservoir benefits from a protected watershed that produces naturally soft water with low dissolved mineral content.
How many people drink Hetch Hetchy Reservoir water?
Hetch Hetchy Reservoir supplies drinking water to 8 cities in our database, serving approximately 2,240,470 residents. The largest cities include San Jose, CA; Fremont, CA; Newark, CA.
Do I need a water filter for Hetch Hetchy Reservoir water?
It depends on your priorities. Hetch Hetchy Reservoir water is relatively clean, but a point-of-use filter can reduce chlorine taste and provide additional contaminant protection.