Every year, the WTCPUA calculates customers’ annual wastewater (sewer) rates using a process called winter wastewater averaging. This method helps ensure your wastewater charges reflect the water that typically enters the sewer system during the months when overall use is lowest. Here’s how the process works and why it matters for your household. 
What Is Winter Wastewater Averaging?
Wastewater averaging takes place during the three winter months of December, January, and February. These months usually represent the lowest household water use because most customers reduce irrigation, pool filling, car washing, and other outdoor activities. This winter period provides the most accurate picture of indoor water use, which is what impacts the wastewater system.
How Your Average Is Calculated
At the end of the tracking period, the usage for all three months is averaged. This number becomes your fixed monthly wastewater charge for the next year. For example: December: 4,000 gallons; January: 4,000 gallons; February: 5,000 gallons; Average: 4,300 gallons per month. That average becomes your wastewater billing baseline.
Why Reducing Outdoor Use Matters During Winter Averaging
Although outdoor water does not enter the sewer system, your meter records all water used on the property. Any irrigation or outdoor watering during these months will increase your total winter water use, which may result in a higher wastewater average. Minimizing outdoor water use during the winter averaging period helps keep your wastewater charges as low as possible.
What Counts as Wastewater?
Wastewater includes anything that flows down indoor household drains, such as showers and baths, toilets, sinks, washing machines, dishwashers, and other indoor fixtures. These flows are collected and treated to protect local waterways, including streams, rivers, and creeks.
Your Rate Won’t Go Up the Rest of the Year
Once your winter wastewater average is set, your fee will remain the same regardless of how much water you use during the rest of the year. This provides stability for budgeting and ensures that wastewater charges reflect typical indoor household use.