Montgomery and Prince George's County residents could see their water bills rise by as much as 9.5 percent starting July 1.

The request by the counties' water provider would raise the average resident's monthly bill by $6.65 to an average of $79.94 and would be the 10th year in a row in which the Washington Suburban Sanitary Commission increased its rates.

The WSSC also anticipates rate increases every year through fiscal 2019, starting with 11.5 percent in fiscal 2015 and decreasing every subsequent year, though spokesman I.J. Hudson emphasized that those rate increases are predictions and could easily change before the agency asks for them.

The Montgomery County Council's staff recommends the agency increase next year's rates no more than 8 percent, which would be a $5.57 increase on the average resident's monthly bill.

Both proposals assume a $506 million increase in debt to pay for what officials generally agree are desperately needed improvements to an aging system. Debt alone accounts for a roughly 4.5 percent rate increase, and combined, all fixed costs account for a nearly 7 percent rate increase.

About a quarter of the WSSC's 5,551 miles of water main are at least 50 years old. By fiscal 2015, the agency intends to start a program that would replace 55 miles of water main a year at a cost of about $1.4 million per mile of pipeline.

In fiscal 2011, there were 34.7 water main breaks for every 100 miles of water main, according to the agency's data. In the current fiscal year, the agency anticipates another 34 breaks for every 100 miles.

But when deciding how much to increase rates, lawmakers should remember the other economic burdens residents are asked to bear, council Senior Legislative Analyst Keith Levchenko wrote in a council memo. He pointed to rising energy and health costs, as well as other county taxes and fees. Several state and county taxes increased on July 1, including the county property and energy taxes and state income taxes.

The council's Transportation, Infrastructure, Energy and Environment Committee is scheduled to take up the issue Thursday, and residents will be able to voice opinions on the issue Tuesday.

The Montgomery and Prince George's County councils will need to agree before establishing the agency's budget for next year and the amount rates can rise. That decision will be made in the spring.