When it comes down to it, learning about various problems with NYC buildings is like an episode of This Old House. Though the the city's Department of Environmental Protection says that the drinking water supply in southeastern Queens is safe, after last week's brief scare when tetrachloroethylene (PERC) was found in higher than normal amounts (though the water was still apparently safe), it turns out that many city buildings lack a special water valve.
The NY Times reports that even though backflow prevention valves are required by city law, thousands of buildings lack them. Backflow preventers help protect water supplies by keeping "hazardous substances from being sucked into the public water system." From the Times:
[C]ity officials identified a car wash as having contributed to the [PERC] contamination at least partly because it did not have the valve installed on one of its water supply lines...
The records also show that about 26,000 buildings in the city represent an especially high risk because factories, gasoline stations or businesses that handle hazardous materials housed in those buildings have not installed the device, called a backflow prevention valve...
The backflow prevention valves are generally located near water meters inside commercial, industrial and large residential buildings. They are attached to water lines completely separate from wastewater lines that run to the sewers, and are designed to prevent contaminated water within a building’s systems from being drawn back into the water mains.
For example, the chemically treated water in a large boiler could flow back into the water supply if water pressure into the building suddenly dropped. The contaminated water then could travel to other buildings.
Oh, gross. The city's enforcement of "backflow valves rules" has been criticized as "lax," even after a task force set compliance goals back in 2000.
However, more buildings than records suggest may have valves, according to the Real Estate Board of NY, but red tape and bureaucracy are keeping buildings from total compliance. And the DEP says that while it will try to inspect more buildings for backflow prevention valves, testing and monitoring the water is the "really the way we assure the public of water quality."
Here's a graphic of how backflow preventers protect water quality. The latest drinking water supply and quality report from the DEP is the 2005 one.