The contrast in drinking water quality on Long Island is exemplified by tests for contaminants at its two largest water utilities - Suffolk County Water Authority, serving more than a million people, and Lynbrook-based Long Island American Water Corp., with 230,000 customers in Nassau County. These two water utilities also rank among the 10 largest in the state.

While tests on water supplied by Suffolk County Water Authority showed levels of regulated pollutants to be within legal and health limits, Long Island American Water Corp. results showed six contaminants below legal limits established by the federal Safe Water Drinking Act but greater than health guidelines, which typically are more strict. These pollutants included heavy metals, radioactive substances and solvents.  Whether these test results violate the law depends on whether repeated tests over prolonged periods of time show the same thing.

The results are part of a three-year project "to create the largest drinking water quality database in existence," said the Washington, D.C.-based Environmental Working Group, whose data The New York Times posted at www.nytimes.com/contaminants.

The vast majority of the 42 water systems in Nassau County showed at least some above normal levels of certain regulated pollutants.  By contrast, in less populous Suffolk County, most water systems for which data was available got a clean bill of health. The one exception was the Smithtown Water Department, serving about 20,000 people, where lead levels were slightly elevated. However, of the 18 systems in the county, the seven smallest -- those with fewer than a thousand customers -- did not submit data.