Suffolk County Executive Steve Bellone signed a bill Thursday allowing the county to approve high-tech wastewater treatment systems to replace septic systems and cesspools.

Standing in front of a Nesconset home where one of 19 pilot systems were installed last year, Bellone called it “key legislation” to reducing nitrogen in ground and surface water from homes that won’t be able to connect to sewers.

“Water quality in Suffolk County and across Long Island is critical to us,” he said.

Under the new portion of Suffolk’s Sanitary Code, Article 19, the county Department of Health can approve nitrogen reduction systems for use by homes and businesses. County health officials said the new systems can reduce nitrogen from wastewater by 70 percent.

The Suffolk Legislature unanimously approved the bill earlier this month.

In addition to the initial round of pilot systems installed last year, another 20 systems will be installed this winter for testing. The houses were selected by lottery.

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Legis. Leslie Kennedy (R-Nesconset) said use of the new systems will be voluntary but urged residents to consider making the change.

The Nesconset homeowner, Jim Minet, 59, said the new system has worked well.

“It’s been seamless,” he said. His system, which would have cost about $12,500, was provided by the manufacturer for free. He said the county conducted testing every month. The first five years of maintenance provided by the county, but would normally cost about $250 to $300 a year.

Kevin McDonald, of The Nature Conservancy on Long Island, said lawmakers will have to tackle how to provide incentives or grants to help residents switch to new systems. The county is also expected next year to consider whether to mandate the use of systems in new construction.