Sewer overflow in river

Sewage Q&A

Are you stumped by sewage? Our new Q&A answers some of the questions you may have about the Great Sewage Debate.

Emily Cooper


We've updated our Sewage Map

The new Sewage Map contains 2021 data for England and Wales, as well as a whole host of new features.

This has been a week of waiting in the Great Sewage Debate. The public and MPs finally have access to more estimates of the cost of cleaning up our sewers, but we are still waiting for the wording for a new amendment that the government says will tackle sewage pollution.

So where are we now? Our Director of Partnerships and Communications, Christine Colvin, has created this simple (and not so simple) Sewage Q&A.

Yes! In England we know that the water companies themselves reported more than 400,000 sewer overspills in 2020. Recent evidence to the Environmental Audit Committee indicates that the real number is likely to be much higher than this.

Combined Sewer Overflows (CSOs), or storm overflows, are designed as an emergency release valve for the sewer network. Many of our sewers are combined, with both rainwater from surface drains as well as foul water from homes and industry. CSOs should only overspill when there’s heavy rainfall and the system is overwhelmed—but in 2020, 45% of CSOs spilled more than 20 times. This was due to: genuinely heavy rainfall; blockages such as fatbergs; sewer capacity lagging behind urban growth; and illegal spills.

Yes – water companies can discharge untreated sewage during periods of exceptional rainfall. They have permits to discharge, and should work within their permit conditions.

We don’t know. More CSOs are monitored now than previously. In 2020, 12,000 storm overflows (80% of the network) were monitored and reported by water companies to the EA, whereas in 2016, it was only 862. While we’ve got a much better picture of what’s happening, until we have a few years at the same level of monitoring we won’t see if the number and duration of spills is increasing or decreasing. Currently, we have event data which tell us how long CSOs spilled. We don’t know the quality of the water and how polluted it is.

No. Agriculture is the sector that accounts for the highest number of rivers failing to achieve good ecological status. 63% of rivers failed because of agriculture. 53% of rivers failed because of the water sector, and the biggest activity causing that failure was treated effluent (treated sewage) discharge. Untreated sewage from storm overflows caused 12% of rivers to fail.

No. In October, the Environment Bill returned to the Commons with amendments from the Lords. One of those was tabled by the Duke of Wellington, and it placed a new ‘Duty on sewerage undertakers to take all reasonable steps to ensure untreated sewage is not discharged from storm overflows’. Environmental NGOs including Blueprint, the Angling Trust, Surfers Against Sewage and The Rivers Trust supported this amendment because it set a clear objective within the new Bill ‘ to try to eliminate, not simply reduce, the harm caused to the environment and individual and public health by the discharge of untreated sewage into rivers’. Despite cross-party support, a majority of Conservative MPs voted against this amendment. They didn’t vote to allow sewage in our rivers, but they didn’t support this clause to stop it.

The Environment Bill has a new chapter on Storm Overflows, which tells government to publish a plan in September 2022, to reduce the harm caused by raw sewage into our rivers.

No. It will cost that amount to dig up all our old infrastructure, where we have combined sewers, and replace it with separate systems. We don’t know how much it will cost us as taxpayers, as water consumers or as shareholders in water companies, to fully remedy the problem. We now have some initial estimates of different options for spill reduction around the country, but they are very broad estimates with low confidence. There are many different ways to solve the problem, and costing them at a national scale is complicated.

Yes! Wet wipes containing plastic block sewers, causing some of the sewage overspills. That’s not to mention the fact that it takes 450 years for them to break down! Non-plastic alternatives are available and can replace the plastic wipes. Fleur Anderson (MP for Putney) has introduced a 10-minute rule Bill to achieve this. Find out more and support this here.

  1. Ask the government to support the Wellington amendment which is coming back to the Commons again on Monday 8th in this petition.
  2. Encourage everyone to write to their MPs, asking them to vote to clearly put a new duty on wate companies to stop sewage pollution
  3. Sign this petition, asking for more resources so that the the Environment Agency can successfully prosecute river polluters.
  4. Only ever flush the three Ps: pee, poo and paper
  5. Start thinking about whether you could help minimise rainwater getting into drains by building soakaways and installing water butts.

Yes – that’s what we’re fighting for. We need to stop pollution from sewage, agricultural slurry, fertilizer, and industry to have rivers that are safer to play and swim in. A river is (hopefully!) alive with wildlife, so it is not a sanitised environment like a swimming pool. Even an ecologically healthy river does not have water that is safe to drink; it will still have bacteria from wildlife. We want unpolluted rivers to swim and play in, but they won’t have water which is safe to drink untreated.

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