Wastewater treatment involves chemical and biological processes that turn raw sewage into environmentally-friendly water.
When a treatment works or pumping station is treating or pumping as much wastewater as it can, any excess flows into storm tanks. These tanks store the wastewater until the flow reduces.
Storm overflows happen when storm tanks fill up so quickly that they literally start to overflow. Wastewater spills over directly into rivers or the sea before it has chance to get treated.
We are working hard to reduce the amount of times overflows happen. By 2025, we'll get them down to an average of 20 per year per location, and by 2030 we'll we'll reduce them further to 17.5 spills per year in any one location.