Combined sewers take both foul sewage from homes and businesses, as well as surface water from roads, to the treatment works.

Being rainwater, surface water doesn't need much treatment before being released back into rivers. Sending it to the treatment works not only wastes energy and money in transporting and treating it, but also risks overloading our pump stations and storm tanks.

By seperating sewers (building one to hold the foul flows and one to hold surface water) we can reduce the flows inside our sewers and reduce the risk of storm overflows. The surface water is released into rivers after going through an oil interceptor.

Infiltration is when surface water or groundwater enters our sewers in places it's not meant to (e.g. through manhole covers).

This means that a lot more wastewater enters the sewers and increases the risk of activating our storm overflows.

To stop infiltration we'll be lining, repairing and replacing our pipes and manhole covers in hotspot areas. We call this rehabilitation work.

Storm water is the number one cause of storm overflows. The huge rainfalls we're experiencing as climate change takes hold are overwhelming our sewers, meaning our storm tanks fill up faster and start overflowing before our pumps have chance to reduce the volume inside them.

We're hoping that our work to reduce infiltration will help reduce the amount of storm water entering our sewers.

But, we're also making sure there's enough storage to hold it all. That's why we're looking into building brand new storm storage near Queen Mary Gardens and The Moor, and we're investigating other potential areas.

By upgrading our treatment works we can reduce the amount of time wastewater stays in our system. We're looking into ways to increase the volume of wastewater that can be treated at any time. A solution will be designed based on the results of our investigations.