Overflow Event Data

We are committed to providing accurate information about the performance of our sewer network as part of our approach to improving water quality in Scotland. 

In our Improving Urban Waters Routemap, published in December 2021, we said we would increase reporting of discharge data from monitored overflows over time:

  • By December 2022 publish annual data for monitored CSOs where data is already reported to SEPA, identifying the main reason for the spills where possible.

  • By December 2023, publish discharge data annually for all other monitored CSOs.

  • By December 2024, publish near real-time discharge data for all monitored CSOs.


What has been published?

We have made available the following data:

  • Overflow discharges included within our annual regulatory reporting to SEPA covering the period 2019-2023. 

  • Discharges from all other monitored overflows covering 2022 & 2023 only where data has been verified. 


The overflows covered are:

  • Combined Sewer Overflows (CSOs, which stop the system from becoming overwhelmed during heavy rainfall).

  • Settled Storm Sewage Overflows (SSSOs, a form of CSO that provides a level of treatment before discharge).

  • Emergency Overflows (EOs, which should only operate in the event of sewer system failure and should not operate in response to rainfall).


Reporting does not include reasons for discharges which Scottish Water does not currently record.

Overflow discharge data in the regulatory return is reported annually to SEPA in line with specific requirements set out within our licenses.

We first published this information on our website in December 2022 (2017 to 2021 data) then updated this in 2023 to include 2018 to 2022 data. 2023 data is now available, and updates will be published annually going forward.

Our commitment to making more data available is one of the commitments in our Improving Urban Waters Routemap. 

As a result, verified data for other monitored overflows, where regulatory reporting is not required, was first published in December 2023 (2022 data). This has now been updated to include 2023 data and updates will be published annually going forward.

As we continue our review and verification processes, we will look to publish data for further monitored overflows where available later in 2024.

The information is available in searchable format by clicking on the blue box at the top of the page and selecting 'download'. 

Discharge data is supported by additional information, including metadata, user guidance, postcode, local authority area, and receiving water.

Overflow Event Data

Download the Scottish Water Reported Overflow Event Data to SEPA 2019-2023 & Summary.

Download here

Other Overflow Event Data

Download the Scottish Water data for other monitored overflows in 2022 & 2023 not reported to SEPA.

Download Here

Improving Urban Waters Routemap

Download the full routemap.

Download here

Combined Sewer Overflow FAQs

Frequently asked questions about combined sewer overflows.

View here

Overflow Monitor

Scottish Water is committed to installing 1000 new monitors over 2024

Additional information 

Please note that this data covers only monitored overflows where data has been quality assured.

Where Event Duration Monitoring (EDM) is a regulatory requirement, we are required to monitor the frequency and duration of releases from overflows. The published overflow data is based on available EDM data.

It’s important to note that the data received from our EDM monitors may not always be accurate. EDM data doesn’t confirm discharges, it only indicates them. For example, the monitors can be very sensitive and can be set off by vegetation movement. Published data is based on a review of the available data which may vary between monitoring locations.

Reasons for discharges are not available for historic events because Scottish Water has not been required to collect or report this information. Scottish Water intends to develop approaches to help identify reasons for discharges and this will become part of future releases of information.

Some parts of the system are operated on our behalf by PFI operators. Where identified as the responsible person for the asset within the discharge license, these operators submit flow and event returns directly to SEPA.

Scottish Water will not publish information other operators report to SEPA. However, as PFI assets return to Scottish Water ownership at the end of PFI contracts, we will then include discharge information from these in our future annual returns to SEPA and this will be subsequently published.

Any grid references within the data set relate to the asset location/monitoring point and not the receiving water.

Find out more about Scotland’s sewers and our improvement plans