Dwr Cymru Welsh Water

Combined Sewer Overflow Monitoring

As part of our Environmental Investigations Programme, we have put monitors on many of our Combined Sewers. These monitors tell us the number of times a Combined Sewer Overflow (CSO) has overflowed which confirms if our sewerage network is operating as it should – it does not measure how much water has been released, the quality of the water that has been released or environmental impact. If a CSO doesn’t work as we’d expect, we’ll investigate to understand what is happening and its impact on the local environment so we can plan any improvements that need to be made.

When combined sewers overflow, the water they release is mostly rainwater so it’s very dilute and unlikely to cause environmental damage. We have permission for this to happen via environmental permits from our environmental regulators, Natural Resources Wales and the Environment Agency.

To make sure this is acceptable to Natural Resources Wales and the Environment Agency, we share and discuss our EDM data with them on an annual basis. They help us decide and prioritise what, if anything, we need to do about the overflows and by when.

The data we submitted to them for 2016 is available on the map below.


Region Map
North West North East Mid Wales South West South East Hereford

Useful Information

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