Greenlawn Water District authorities Sunday advised their 42,000 customers that their water is again safe to drink from the tap, after several days' warnings that water should be boiled due to a rare E. coli bacteria contamination.
Authorities said the water's taste - often rated among the region's best - will change slightly for an indefinite period, because chlorine was added as a precautionary measure.
The district, serving homes and businesses in Greenlawn, Commack and part of Dix Hills, lifted the alert after two days of tests found no further evidence of E. coli. The alert was posted about 4 p.m. Thursday. Water from the district's Well No. 16, located near the intersection of Wicks and Larkfield roads, was found to be contaminated and shut down immediately, officials said.
Dennis Kelleher, an expert water consultant who serves as an engineer for Greenlawn and other districts, said he hadn't encountered another case of E. coli contamination in a public-supply well in 20 years on the job. He said the cause couldn't be determined until a television camera is lowered into the well to inspect its casing for cracks, which requires about 10 days.
"It is extremely rare to get a finding of E. coli from a well this deep," Kelleher said.
The presence of E. coli indicates possible contamination by human or animal waste. Drinking contaminated water can cause diarrhea, nausea or more serious illness.
The 650-foot well, installed in 1994, drew water from the underground Magothy Aquifer. Kelleher said contamination might have come from a point above the aquifer, possibly through a crack in the well casing.
Greenlawn Water gave out about a thousand cases of free bottled water, officials said. Many district residents bought bottled water on their own, and some complained authorities were slow to get out word of the contamination.
Evidence of possible contamination was collected Wednesday during routine sampling of faucets, authorities said. Kelleher said additional time was then needed to check water samples from wells, await lab results and get approval of a boil-alert from county health officials.