It would be the first desalination plant on the Hudson River, converting the brackish waters of the lower Hudson salted by ocean tides into fresh water that the residents of Rockland County would drink.

But county residents are infuriated by the plan to spend $150 million building the plant, with 26,000 people signing petitions to block construction. For one thing, opponents say, there is no need. Rockland County receives, on average, 49 inches of rainfall annually, one of New York State’s highest amounts, they say, adding that there are ways short of desalination to either provide or conserve water.

As important, they say, the plant location on Haverstraw Bay is three and a half miles south of the Indian Point nuclear power plant. Critics say the desalinated water will contain trace amounts of radioactive particles like strontium 90 that they and their children will consume for their lifetimes. The local water utility says the water would meet all federal and state standards.

On Thursday, the state’s Public Service Commission is scheduled to decide whether there is a need for desalination. The ruling could set the stage for the plant’s development by United Water New York, the utility that supplies 90 percent of Rockland’s water (the villages Nyack and Suffern have separate systems) and a portion of Orange County’s, serving a total of 300,000 residents. The Rockland Water Coalition, which includes environmental groups like Riverkeeper and Scenic Hudson, has called on the commission to state clearly that there is no need.