Sewage includes all of the waste which enters sewers from our drains. This can include toilet waste, shower/bath waste, outside drains, and even waste from appliances like washing machines. All of this goes to water treatment plants like the one in the video below.
These treatment plants have a certain capacity they are able to treat and purify. Once this limit is exceeded, possibly due to increased rainfall, there are two options. Firstly, large storage containers can be used to store raw sewage until there is capacity to treat it. Alternatively overflow solutions are used to release waste into nearby water systems.
These storm overflows are a result of Victorian sewer infrastructure design to help when the system is over capacity. They prevent sewage from backing up into homes and spilling out onto streets. An increase in heavy storm events, an increasing population, and more impermeable infrastructure is increasing the strain on the already struggling system.
In England there are about 15,000 storm overflows with 90% of them discharging in 2021 and 5% of these discharging over 100 times. The discharge can contain harmful pathogens posing a large threat to those using the water for recreation.
As of February 2025 only 4% of storm overflows in Scotland are monitored and Northern Ireland Water has said they don’t have the ability to monitor their overflows at all suggesting they may be used far more often than we know. In England 100% of overflows are monitored, this information has been used to create ‘Sewage Maps’
Sewage Maps, created by Alex Limp and Jonny Dawe, provides real time information about when sewage overflows are discharging. Have a look at it HERE.
Further Resources:
Sewage Maps – A website showing current usage of sewage overflows within England
Swimmers Against Sewage – SAS are a lobbying organisation aimed to change policy to improve water quality in the UK. Here is there annual report from 2023 providing more data on the status of current sewage discharge.
Water UK – More information on how and why sewage is treated before release into the environment.
Swimming with Sewage 