Here’s how to keep this year’s sewer costs down: It’s simple. Trim your water use! You’re charged for sewer based on the amount of water you use. We look at your water use from Dec - Feb when it’s colder & rainier and you irrigate less. We estimate 75% of the water you use during those months goes down the drain, not on your yard. So we take the average of your water use those three months and calculate your sewer bill to be 75% of that. That amount establishes your bill for the next year.