The Riverton City Council recently voted to raise water rates 26 percent, turning down a proposal to double current rates to pay for improvements in the city's water system, officials said.

The improvements include laying a new 18-inch main to increase water pressure and replacing old lead pipes under a federal Environmental Protection Agency mandate, city administrator D'Arcy Dixon Pignanelli said.Current minimum monthly charges of $4 for 5,000 gallons plus 30 cents for each additional 1,000 gallons will be increased to a minimum $5.55 charge and 35 cents for each additional 1,000 gallons, she said.

Laying a new 18-inch diameter line will take $285,000 from water department budget reserves, to be replenished with $30,000 annual payments from the rate increase, Councilman Terry Wright said.

The increase was made to meet increased demand for water in Riverton, which is growing rapidly and may see 100 new connections in 1988 and 1989, said Wright, the plan's originator.

"We were getting to the point where we were having occasional brownouts" (periods of inadequate water supply), Wright said.

The city presented the proposal to double water rates at four town meetings, but residents said "they weren't ready" for a 100 percent increase in water rates and agreed to postpone some water system improvements, Dixon Pignanelli said.

Riverton has a five-year plan to develop its water department to deliver water more effectively, Dixon Pignanelli said.

Other projects, like digging a new well, further expanding the new 18-inch main and upgrading other water lines must be postponed under the plan, Wright said.