Eli5: If a town in the UK gets flooded by local rivers due to storms, does some of the flood water end up going to sewer, and if so does the sewerage plant cope?

Question

Title, a bit in depth – would preferably like someone who works at one, thanks in advance

In: 7

Answer 1

Most municipalities would have two completely separate sewer systems

* a *storm sewer* system, which collects rainwater from streets and other property. These drain down the catch basin (also called storm drains) grates that you would see along the curb on a street. That water flows pretty much untreated back to waterways like lakes or rivers. More stringent standards will now sometimes require some treatment on the property to settle out silt, sand and solids before the water enters the storm drains.
* a *sanitary sewer* system, which takes grey water (sinks, tubs, floor drains and showers) and black water (toilets) and transports it to a sewage treatment plant. In that plant, it is purified and eventually released into a natural waterway.

Generally, a storm sewer system would carry most of the flood water to where it needs to be disposed of. Some will definitely get into the sanitary sewer system, particularly in bad flooding and that excess could certainly overwhelm a sewage treatment plant. If that is the case, then the plant deals with it by releasing it untreated to the waterway. There is little option in this regard – sewage treatment plants aren’t designed to “stockpile” additional volumes. However, in the case of flooding that water is basically rainwater anyway.