The combined sewers mean that much as 95 per cent of the liquid that overwhelms treatment works can be simple rainwater.
Sewage networks are designed to discharge into rivers and the sea when too much water is passing through them One of the largest early successes has been a project to roll out modified water butts to the village of Havenstreet on the Isle of Wight. The storage butts have a narrow drain fitted halfway up, allowing it drain slowly over several hours, reducing the rush of water into the sewers and ensuring both the capacity to catch further rainfall and that the customer still has water in their butt.
For now, the costs are prohibitive for a large-scale deployment, although Southern Water hopes to place them on large industrial sites, stimulating a market and bringing down costs.