The days of Rohnert Park having the cheapest sewer rates in Sonoma County are numbered. Starting next month, home and business owners in the city will pay about seven percent more on their monthly sewer bills. Rates for single-family homes will be increasing by a little more than three dollars during the first five years of planned rate hikes. The second rate increase will take place in July of 2025. Additional rate increases will happen each July through 2028. Cotati will take the title of having the cheapest sewer rates in Sonoma County.