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 2021).

 

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 fluctuate 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.

During 2020, the impact of the pandemic – including restrictions on leaving home, travel and businesses – affected the flow patterns at several of our treatment sites, particularly during dry weather.

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

Flow data 2020

CSV data files for 2020 are also available for each county: Kent, Sussex, Hampshire, Isle of Wight.

Flow data 2019

CSV data files for 2019 are also available for each county: Kent, Sussex, Hampshire, Isle of Wight.

Flow data 2018

CSV data files for 2018 are also available for each county: Kent, Sussex, Hampshire, Isle of Wight.

Flow data 2017

CSV data files for 2017 are also available for each county: Kent, Sussex, Hampshire, Isle of Wight.

Flow data 2016

CSV data files for 2016 are also available for each county: Kent, Sussex, Hampshire, Isle of Wight.

Flow data 2015

CSV data files for 2015 are also available for each county: Kent, Sussex, Hampshire, Isle of Wight.

 

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.

The latest figures published demonstrate our continued progress on supplying more – and more accurate – data on CSO releases to regulators and the public. The number of reported releases has increased since last year but it should be remembered this is highly weather dependent and 2020 saw an increase in rainfall, February was the wettest on record. We have also worked hard to improve our reporting accuracy and have reported on an increased number of permitted locations in 2020.

One big change between 2019 and 2020 is the new ASPIRE spills reporting system which came into service in Dec 2019 and has continued to be improved in 2020 and this will continue in 2021 too. By the end of May all 83 of the region’s designated bathing waters plus Chichester and Langstone Harbours will be covered by the near-real-time Beachbuoy information service which is another reflection of our commitment to openness and transparency.

Storm releases are made for one reason – to protect homes and businesses from flooding. For instance in heavy rain, storm releases from our Budds Farm wastewater treatment works (and the related CSOs) protect more than 2000 properties including schools and hospitals.

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

Spill data 2020 – Excel

Spill data 2020 – CSV

Spill data 2017–19 – Excel

Spill data 2017–19 – CSV


Key

The acronyms used in the data files have the following definitions:

  • CEO – Combined Emergency Overflow: A storm overflow and an emergency overflow from a wastewater pumping station that discharge via the same outlet.
  • SSO – Settled Storm Overflow: An overflow designed to discharge heavily diluted and settled wastewater via an outfall pipe directly to controlled waters, when flows to a wastewater treatment works exceed the pass forward rate capacity for the site and the storm tanks are full, due to rainfall and/or snowmelt.
  • EMO – Emergency Overflow: An overflow at a wastewater pumping station which allows spillage of foul sewage to a watercourse or other waters in an emergency, in the event of mechanical or electrical failure of the pumping station, or due to failure of the downstream rising main.

 

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.  

 
 
 
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