The city has said it will not increase water and sewer rates through the end of June 2013. “We decided that the city could afford to absorb the modest increase in what water costs us, and that holding the line on water rates would be something that benefits everyone in the city,” said Mayor Joseph Curtatone in a statement. “It's a way for us to help ratepayers still dealing with the tough economic times that we have all been experiencing over the last few years.” Somerville relies on the Massachusetts Water Resource Authority for water. The group charges the city, which in turn bills residents. The rate charged by the authority increased this year by 2.6 percent, Curtatone said.