If the Massachusetts Water Resource Authority approves a proposed water-sewer rate increase in June, Milton families could see water bills rise 8.5 percent, under the MWRA’s estimated 2012-13 assessments. Assessments are based on local use, and MWRA officials said Milton uses about twice as much water as surrounding towns of its size; thus, Milton’s increase would be more than double the average of 3.9 percent. The increases would raise the wholesale price of water and sewer services to communities the MWRA serves and are part of a three-year strategy that began last year. Two public hearings on the increase will occur before the final vote in June, and MWRA officials said last week that numbers may change, though only slightly. - Natalie Feulner