When I open the tap, water comes out. But from where?

85% comes from Hetch Hetchy in Yosemite. Spring snow melt from the Tuolomne River fills Hetch Hetchy reservoir. This surface water in the Hetch Hetchy Reservoir is treated, but not filtered because it is of such high quality.

15% comes from the Alameda and Peninsula watershed. The supplies are stored in Caleveras and San Antonio reservoirs. In addition, the Crystal Spring reservoirs on the Peninsula store excess Hetch Hetchy supplies.

Let’s talk treatments. Almost all water in this country is filtered and treated with chlorine. Not so true here in SF.

Hetch Hetchy water has been granted an exemption by the state, thus no mechanical filtration is applied. Most waterborne illnesses are caused by bacteria that range between 1-5 microns. The two biggest culprits are Cryptosporidium and Giardia. The best method for removal is mechanical filtration. Even though very few cases of waterborne diseases are reported in SF, a sudden spike in pathogen levels is a potential risk.

In terms of disinfection, San Francisco for years used chlorine. The EPA has approved one other disinfectant: chloramine, a mixture of chlorine and ammonia. San Francisco switched to chloramine in late 2004, mainly in response to elevated TTHM levels found. TTHMs, total trihalomethanes, are a group of compounds generally created when chlorine reacts with organic pollutants….many TTHMs are considered carcinogenic. Chloramine does not dissipate as quickly as chlorine, lending to increased allergy risk and complaints re: taste. There is a second by-product of concern from chloramine, NDMA (N-nitrosodimethylamine). NDMA is considered highly carcinogenic and is being investigated rigorously by the EPA. NDMA concentrations in SF are way below the current EPA guidelines.

Lastly, there is the issue of metal contamination. The chief concern in SF is lead, mainly from old faucets and plumbing. Lead is mainly a health issue for pregnant women as it is linked to certain birth defects. Faucets made before 1997 included as much as 8 percent lead, creating much of the problem. FYI…The SFPUC does offer a program selling lead-free faucets for $10.