SEWAGE: WHY IS RAW WASTE PUMPED INTO OUR SEAS AND CAN WE FIX IT?

The UK's ageing infrastructure is struggling to cope with increased rainfall and a growing population, and this means sewage is being discharged into our seas and rivers. Just when you thought it was safe to go back into the water...

-  JOCELYN TIMPERLEY

Recent months have seen fresh concerns over a wave of discharges of untreated raw sewage in the UK. In early September, the Safer Seas and Rivers Service, which is run by the charity Surfers Against Sewage, issued pollution warnings for more than 100 beaches. Rising awareness of these events has led to public anger about the situation. But why is this happening now, and what can be done about it?

Unlike some other countries, which have split drainage systems for rainfall and sewage, the UK has a combined system that accepts both. It's managed by water and sewage companies, who, if all is well, biologically treat the sewage before discharging it into the environment. But under extreme circumstances, such as exceptionally high rainfall, these companies are allowed to discharge untreated sewage. This is to avoid capacity being reached and sewage coming back into people's homes and businesses, says Dr Sarah Purnell, a researcher in aquatic environment health at the University of Brighton.

The legal model works relatively well when these events happen infrequently, notes Purnell. And since the sewage is mixed with stormwater on these occasions, it should be highly diluted.

The problem is that these legal discharges are happening far more than many people realised and may be more concentrated. Michelle Walker, technical director of The Rivers Trust, says overflows of untreated sewage are being routinely used even when it hasn't been raining.