Atlanta water users, brace yourselves for yet another costly hit.

The average water/sewer bill will jump $21 a month in July and climb 70 percent over the next four years under a rate plan the City Council approved Thursday.

The increases come on top of similar rate hikes the 15-member council imposed in 2003. When they are all in place, the average water bill will have jumped from $50 to $143 per month – a 186 percent increase – over a decade.

The new rates affect Atlanta residents and people who live in south Fulton and Sandy Springs and use city services.

Council members approved what the Department of Watershed Management said was needed to keep afloat Clean Water Atlanta, Mayor Shirley Franklin's $4 billion program to overhaul the city's aging water and sewer systems. The vote was 13-0.

Council members said they didn't believe they had any other choice. Watershed officials stressed during a work session Wednesday that any reduction in revenues could leave the department in default on billions of dollars in outstanding bonds.

"This is a very tight program," said Councilwoman Clair Muller.

The council turned back an effort by Councilwoman Mary Norwood to set the rate for just one year.

Councilwoman Natalyn Archibong said a four-year schedule was better for bond agencies that monitor Atlanta's finances and residents who must budget to pay the bills. "We knew there was going to be an increase," she said.

Much of the debate Thursday concerned an audit of the watershed department that the council had demanded before it would approve a rate increase. But the council backed down and agreed to give the department its requested rates for four years as long as the audit gets done this year.

The water/sewer rate hike comes on top of a property tax increase and several service cuts Franklin has proposed for the fiscal year that begins July 1. Franklin's proposed tax hike would cost the owner of a $200,000 house about $24 a year. The water/sewer rate increase will cost about as much every month.

The money generated from the rate increase will be used to pay bonds and support the water/sewer overhaul. The mayor once touted the program as a $3 billion effort whose costs would be shared equally by rate-payers, Georgia and the federal government.

However, Atlanta has received just a few million dollars in federal grants and only loans from the state government.