A complex system necessary for safely and efficiently moving wastewater
Our wastewater collection system is designed and built to collect and convey wastewater from homes, businesses and industries in all corners of our service area to our Nine Springs Wastewater Treatment Plant in south Madison. Any water that is used for washing, flushing or industrial processing is considered wastewater. Once the water becomes contaminated or is otherwise unfit for human consumption, it is considered wastewater.
How the system works
Our service area’s wastewater collection system is a complex maze of pumping stations and pipes; these pipes get progressively larger as they move closer to the treatment plant. The District owns and operates 142 miles of pipe and 18 regional pumping stations. View an interactive collection system map here.
When wastewater leaves a home or business through a drain, sink or toilet, it first travels through a sewer lateral before connecting with a local sewer pipe. In most communities, property owners are responsible for their own sewer laterals, and for some property owners, regular lateral cleaning may be necessary to prevent sewer backups.
Once the wastewater moves into a local municipality’s sewer pipe, it eventually flows to a District interceptor, which is a larger sewer pipe that collects wastewater from a number of neighborhoods and communities. Where the terrain allows, we convey wastewater through gravity sewer lines, which use gravity and the natural slope of the land to move wastewater through the system. This is also why wastewater treatment plants are often located in a low point of a service area.
When gravity flow in the collection system is no longer possible, pumping stations are needed to push the wastewater from a lower elevation to a higher elevation. The pumps at these stations use mechanical energy to move the wastewater uphill through pressurized pipes called force mains. Eventually, the wastewater from the force mains is discharged back into the gravity pipes at high points in the system and the process is repeated until the wastewater reaches the treatment plant.
The collected wastewater feeds into the treatment plant for processing. Learn more about this process on our Wastewater Treatment page.
Your role in the system
Inflow & infiltration
The District’s collection system conveys approximately 41 million gallons of wastewater to the plant daily. During heavy rainfalls, this amount may peak due to inflow and infiltration (I/I), which is when clear water like rain or groundwater gets into the system through cracks in pipes, damaged manholes or improper sump pump use in homes and businesses. Through collaboration with some of its owner communities, the District has developed an I/I program that it is rolling out over the next few years. To learn how you can support this work and reduce I/I on your property, visit our Inflow & Infiltration page.
Love your pipes
Only human waste and water should be flushed in toilets or put down the drains in your home or business. Improper disposal of non-flushable or unflushable items – such as wipes, dental floss, diapers and tampon applicators; or fats, oils and grease from kitchens – can result in expensive and messy sewer backups in your home or business. Nonflushables can also cause problems in the collection system by blocking sewer pipes, damaging pumps, and requiring extra cleaning, which results in higher costs to users of the system. Learn more about what not to flush on our Nonflushables page.
Similarly, the sewer system is not the place for pharmaceutical waste or household wastes. Please dispose of these items responsibly.