The state Public Service Commission on Thursday approved Liberty Utilities’ request for a three-year rate increase that will increase water bills for more than 120,000 Nassau customers by as much as $19 a month starting next month.

The state-approved rates, which take effect Sept. 1, will affect customers from Sea Cliff to Merrick to Atlantic Beach to varying degrees. Many will see a $19.25 increase in their September bills. Liberty (New York Water) Utilities bought the system from New York American Water in 2022 for $608 million after years of customer complaints about the rates.

Public Service Commission Chairman Rory Christian said in a statement that the approved tariff plan “ensures critical investments that will positively impact the tariffs paid by customers and assure them of a safe and adequate service.”

But longtime water utility critic David Denenberg called the rate increase “repulsive” and said it confirmed his belief that only public water supply could lower rates and improve quality.

“We need a tax-free, high-quality public water supply instead of expensive, low-quality, investor-owned monopoly water,” said D Enenberg, co-chair of the activist group Long Island Clean Air, Water, Soil.

Newly formed water authorities on the North and South Shores in Liberty’s territories are attempting to take over parts of the system, including most of it in the Town of Hempstead, but the efforts have been slow and met with mixed success.

In a statement, the PSC noted that the possibility of fully public water supply “remains for at least a portion of the Liberty system.” Newsday reported last month that the South Nassau Water District recently submitted a bid for most of the system in Hempstead.

The rate increases approved Thursday were part of a deal reached earlier this year with the PSC’s administrative arm, the Department of Public Service. They would increase bills in the Lynbrook area and some service areas in the north of the state by a total of 45% over three years, and in the Merrick and Sea Cliff areas by a total of 18% starting in September.

Customers in Service Area 1 will see price increases of 17% starting this year, 15% next year and 13% in 2026, according to the state. This area includes customers in Atlantic Beach, Baldwin, Cedarhurst, East Rockaway, Hempstead, Hewlett, Hewlett Bay Park, Hewlett Harbor, Hewlett Neck, Island Park, Lawrence, Lynbrook, Malverne, Mill Neck, Oceanside, Roosevelt, Valley Stream and Woodmere. Customers with a current average bill of $66.48 will see an increase to $85.73 this year, $98.84 next year and $105.85 in 2026, the state said.

Customers in the Merrick and Sea Cliff areas will see a rate increase of 9.2% this year, 4.5% next year and 4.5% in 2026, according to DPS. The plan includes a catch-up surcharge for delaying the 2024 increase, which Liberty originally planned to pursue in April.

For customers in Merrick with a current bill of $50, bills will rise to $54.91 this year, $57.56 next year and $58.47 in 2026. In Sea Cliff, average monthly bills of $77.98 would rise to $87.72 this year, $90.56 next year and $92.34 in 2026.

The new rate plan will be valid until March 31, 2027, the PSC said, noting that property taxes were among the top three drivers of the increase in Service Area 1 after infrastructure improvements and operations and maintenance costs.

Liberty had originally sought a larger rate increase that would have raised $39.7 million from customers in all areas in the first year. The increase approved by the PSC reduced that amount to $17.24 million.

Liberty did not immediately respond to a request for comment. The PSC said the increase includes health and safety provisions, to pay for lead service line replacement, to create new customer care and delinquency management programs and to allow Liberty to implement an enhanced water conservation program.

Mark Harrington, a reporter for Newsday since 1999, covers energy, wineries, Indian affairs and fisheries.