Flow and Spill reporting

The amount of wastewater leaving our treatment works is measured and often referred to as ‘flow’. If our network becomes overwhelmed, we must release settled and/or screened wastewater at times to protect homes and communities from flooding – this is called a spill.

We publish our annual flow and spill figures here (last updated March 2020).


Our flow data

We report our flow data annually (calendar year) to the Environment Agency. The graph below shows the total amount of treated water that left our sites each year in cubic metres, divided by county.

As the population of our region continues to grow, the volume of wastewater received by our sites increases too. As a result, our flow figures fluxuate year-on-year based on the number of people who choose to live in the South East.

Although this would suggest our flow should increase year-on-year, other factors impact our flow too. For instance, some of our sewers carry rainwater away from gutters and street gullies to our treatment works to prevent flooding. As a result, our flow is also higher during years with a wet winter.


For more detailed daily flow information, divided by site, please download the .xlsx spreadsheets below.

Flow data 2019

Flow data 2018

Flow data 2017

Flow data 2016

Flow data 2015


Our spill data 

What is a spill?

In some areas, sewers are ‘combined’ meaning rainwater from gutters and street gullies is also channelled to our wastewater treatment works during a storm to protect properties and streets from flooding.

If our wastewater treatment works receives more rainwater and wastewater than we're able to process or store, our network could back up which could cause flooding via manholes, drains and toilets. To prevent this, where we can, we store and filter the surplus through a screen before releasing it into the environment – this is called a spill.

Water companies are permitted by the Environment Agency to only spill under strict conditions in order to protect homes, protect the environment and manage storms.

Sometimes, we also have to spill if wastewater stops moving through our network – for example, due to a pump failure. Again, wastewater with nowhere else to go can flood homes and communities, so we release it to prevent this happening.


Total number of spills per county, per year

We report our spill data annually (calendar year) to the Environment Agency. The graph below shows the total number of spills from our wastewater treatment sites each year, divided by county.

Spills are more common during severe weather events. Our region has experienced several periods of intense, heavy rainfall in recent years which has led to more frequent spills.

For more detailed information about spills that occurred during each calendar year, including the location and trigger, please download the .xlsx spreadsheets below.

Spill data 2017–19


Why spills happen 

If you'd like more information about why water companies are permitted to spill, read more about the role of spills in protecting homes and managing storms.  

Close agent lightbox  Close box