Sewage and rainwater  

In cities and towns, rainwater ends up in the municipal sewer system. It can be transported in two ways: via a combined sewer system or via a separate sewer system.

Combined sewer system

A combined sewer system is a system of pipes in which domestic wastewater is collected together with rainwater and transported to a wastewater treatment plant.

  • A major disadvantage of this system is that its capacity is limited. When there is heavy rainfall, the sewer fills up with regular wastewater from households and businesses, as well as rainwater. When the pumps at the sewage pumping station are running at full capacity and the sewer system is filled to maximum volume, the sewer overflow starts to work. A sewer overflow is a facility that allows sewage to be discharged directly into a pond, canal, or river when the sewer system is overloaded.
  • Part of the system's contents is discharged into surface water. These overflows have little impact on water quality, as the wastewater is largely diluted with clean rainwater. Combined sewer systems are particularly common in older neighborhoods and village centers.

Separate sewer system

A separate sewer system is a system of pipes in which rainwater from paved surfaces is collected separately. This clean rainwater does not go to a sewage treatment plant, but is discharged directly into surface water. Wastewater from households and businesses is transported via a different pipe system to a sewage treatment plant.

  • There are not many separate sewer systems in the Netherlands. Simply because they were not often installed in the past. A separate sewer system places quite a few demands on the (current layout) of the environment. That is why it is not always obvious to install them. Moreover, installation is a costly business. Separate sewer systems are installed when renovating existing combined sewer systems and when constructing new sewer systems.
  • The water authority together with municipalities, water authority working hard to limit the supply of uncontaminated rainwater in areas with a mixed system. We do this by disconnecting these water flows from the sewage system as much as possible. In this way, we prevent sewer overflows.