Santa Rosa's Board of Public Utilities approved 3 percent increases to water and sewer rates Thursday.

The changes would cause the average single-family combined summertime water and sewer bill to rise by $4.68 a month next year, to $157.04, and $4.86 a month in 2015, to $161.90 a month.

The increases are needed to fund higher water costs and major improvements to the city's wastewater treatment plant. The city is planning a $16.5 million bond sale in 2014 to upgrade the Llano Road plant, which was built in the 1970s.

The new rates increase the fixed monthly charges slightly more than the usage rates because the city is trying to reduce the wild swings in revenue that can occur when water use changes, such as during a drought.

The City Council will study the proposed increases Nov. 19 and could adopt the new rates following a public hearing Jan. 7.