How clean our rivers are has become a hot topic in recent years, as it has been revealed that untreated sewage has been released into our waters at alarming frequencies. A freedom of information request by the Ferret last year found that, in 2020, sewage had spilled out into Scotland's waterways 12,000 times. 

In August last year, Scottish Water reported that in the period from 2016 to 2020, spills had increased by 40 percent. In those five years the equivalent of 47,000 swimming pools of sewage had entered the water.

Many of these happened through combined sewage overflows, which are designed to release untreated sewage in times of extreme rain, are less monitored in Scotland than in England, with only 10%of them monitored here, compared to 80% in England.

The result is that we don't know exactly how much untreated sewage is entering the water - but we do know that it's happening at alarming rates in some rivers.  For instance, when in 2021, Alison Baker of Forth Rivers Trust put in  a freedom of information request to find out what untreated sewage had been dumped into the river in 2020, she found that, though SEPA’s data was incomplete, there were at least 617 untreated sewage dumping events, in which the equivalne of 121 Olympic swimming pools of waste entered the water.

In an in-depth Herald magazine feature, Baker described her horror, saying, “If a sewage overflow happened once a year in a big flood. I’d think, ‘Oh, okay. I don’t want people’s homes flooding. But if it’s happening every week and the river is not high, then that’s wrong.”

READ MORE: Busted Flush: My journey through Scotland's sewage


So what is Scottish Water doing to solve the problem? A spokesperson gave us the following answers:

Q: Last year it was reported that spill events were up 40 percent on 2016, why is that?

Scottish Water: These are the summary figures on spills over the last 6 years.

The Herald:

Note that these are spills only at the assets that we are required to report on and not the full number of spills across all of our assets. While the 2020 figure is higher, the 2021 figure is in line with the average number of total spills. We don’t have a singular reason for this. Changing weather patterns, rainfall patterns, the intensity of rainfall events and the localised nature of some events all have an impact.

Piped drainage systems have a finite capacity, during severe rainstorm events, manmade drainage systems (such as sewers, culverted watercourses and road drains) are often temporarily unable to cope with the volume of surface water they receive in a very short period of time.

Q: What actually triggers an untreated sewage release? 

SW: During heavy rainfall storms, more water is getting into our sewers than they have been designed to cope with. Combined Sewer Overflows (CSOs) have been included as a relief mechanism to safely relieve the pressure on the network which greatly reduces the risk of sewer flooding in streets and in customer homes. These CSOs and are licensed by SEPA and storm water is automatically released over a weir or other control device into an overflow pipe, which discharges at designated locations into watercourses or the sea.

The Herald:

Q: What is being done to reduce the frequency of these releases/"spill events"?

SW: In December, we released our Urban Waters Route map which sets out how we will: • Improve water quality by improving some CSOs (to support Scotland’s RBMP objectives).

• Increase monitoring and reporting to cover all combined sewer overflows (CSOs) that discharge into the highest priority waters.

• Significantly reduce sewer related debris in the environment by improving other CSOs, and • Progressively introduce interventions which will reduce spills from the sewer network Details on this can be found here: Urban Water Routemap - Scottish Water 4.

Q: You recently, through your Nature Calls campaign, called on the public to stop putting wet wipes down toilets and for a ban on wipes containing plastic. What else might be done?  

SW: We cannot simply engineer our way out of the issue presented by climate change, for example by building bigger sewers. We are focusing on developing solutions which will keep surface water out of the sewers. These include increased use of Sustainable Urban Drainage Systems (SUDS) which will help manage surface water effectively and more sustainably rather than it simply being channelled into sewers.

We are currently in the process of adopting 1400+ SUDS to take them fully into public ownership as part of the approach to managing waste water and reducing flood risk. These have wider benefits for environment, community and help reduce flooding.

Several projects (St Mary's in Dundee) underline how effective these can be (also raingardens in Glasgow) - the concept of rainproofing is something we are keen to develop, working with communities and partners. If you need anymore information on these, please let me know.

Q: Will there always be some sort of untreated sewage release? Is it part of the system and we just have to acknowledge it?

SW: CSOs are an integral part of the existing sewer systems. We continue to invest heavily and look to develop blue green infrastructure initiatives to manage surface water more effectively and take pressure off the combined system. For example, the surface water from all new housing doesn’t drain into the combined system and is separated from foul flow and managed using SUDS. We are working with a number of partners to implement new types of initiatives to manage storm water on the surface, ie the Glasgow Smart Canal initiative.  

We won’t solve the CSO and resulting debris issues ourselves and changing customer behaviour around what is washed down the sink or flushed down the loo is really important. However, some spills are always likely to occur and by keeping debris out of the sewerage system, it won’t end up in the environment.

Q: What are the current plans to increase the monitoring of CSOs? I read 12 percent by 2024. Has this changed?

SW: Our Urban Waters Routemap outlines our ambition to install 1000 new event and duration monitors where CSOs are discharging to the highest priority waters which is estimated to cost between £50 million and £70 million.

Q: Does all this stuff we put down our drains increase the likelihood or impact of a CSO release?

SW: Absolutely. Wipes, nappies, fats, oils, sanitary products and more cause blockages that lead to spills causing environmental and flooding events, impacting customers and businesses.