Connecticut utility regulators on Tuesday approved an 8.6 percent increase in water rates for the Aquarion Water Co. of Connecticut, which provides water service in Stonington and Mystic and several other towns elsewhere in the state.

The state Public Utilities Regulatory Authority said in a news release that Aquarion requested a rate increase totaling $26.9 million, but that the authority granted an increase that was $13 million less.

Aquarion will spread the increase over three years, PURA said. The company argued that the increase was needed for infrastructure improvements and depreciation expenses. It also said the rate increase was necessary because of declining consumption and cost increases outside its control.

PURA's ruling scales back proposed inflation-related expenses, increases Aquarion's sales forecasts, and cuts requested acquisition and pension costs, the agency said. It also makes cuts in proposed director and officer liability insurance costs, disallows ratepayer recovery of charitable contributions, and halves Aquarion's proposed employee bonus plan expenses.

The 8.6 percent increase will include a 2 percent infrastructure surcharge, PURA said.

Aquarion Water Co. is the largest investor-owned water company in Connecticut and in New England. It provides water services through 79 systems to more than 185,000 customers in 47 towns and cities in Connecticut. For the fiscal year ending December, Aquarion had operating revenues of $156.8 million and net utility plant of $769 million.