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Sewers, blockages and water pollution

Sewers, blockages and water pollution

Information on pollution and blockages of sewers and watercourses.

If you witness a pollution incident on a river, notify the Environment Agency incident hotline (opens new window) immediately.

Surface water sewers 

Surface water runoff has an impact on the water quality of the river. This is due to surface water picking up contaminants ,as it drains from the urban landscape and flows into the river. 

Where does surface water pollution come from?

  • Your house: Incorrect plumbing could mean that waste water from dishwashers, washing machines, sinks, baths and even toilets is flushed directly into a local river. People doing their own plumbing and even professional plumbers can accidentally create these misconnections, which are a common cause of pollution to rivers and streams, especially in towns and cities. 
  • Your driveway: When you wash your car in the driveway or on the street, the dirt, oil, and detergent laden water runs into drains and then directly into our streams, rivers, and lakes. Just as soap destroys dirt and organisms on your car, it will do the same in rivers and other bodies of water. Many of the commonly-used soaps contain phosphates, which remove oxygen from the water. 
  • Car parks: These can be a big risk, as they are often contaminated with oil, petrol and toxic metals from cars. In heavy rain, all of this pollution would be washed off into drains, polluting nearby watercourses.
  • Agriculture: In more rural parts of Hillingdon, chemicals being sprayed on agricultural land, such as pesticides and herbicides, can find their way into watercourses from spray drift. This can also affect hedgerows and other habitats bordering the sprayed area. Pesticides especially can have serious effects on aquatic life. All of this pollution ends up flowing into the Crane and the Colne Rivers. 

Foul sewage

Everything that goes down the kitchen, laundry and bathroom sink or that's flushed down the toilet ends up in the sewerage system. Treated sewage is either reused or safely returned to our rivers and oceans.

Putting the wrong things down the sewer affects our ability to treat and reuse the water and can cause damage to the system. According to Thames Water, more than half of blockages are caused by fat and cooking oil. These 'fat bergs' can cause blockages resulting in flooding.

What you can do to help

  • Plumb in new appliances correctly. Ask for a WaterSafe plumber (opens new window).
  • Check your home for existing misconnections and get them fixed.
  • Don't use toilets as litter bins or pour oil or fat down kitchen sinks.
  • Don't pour paint or throw food waste down surface water drains that lead to rivers.
  • Get involved in work across London through Thames 21 (opens new window)
  • Promote the use of permeable surfaces to reduce runoff from paved areas. This reduces the pollutants entering watercourses, and allows some pollutants to be broken down on site.

For information about current projects to help improve our rivers, visit the Colne Catchment Action Network (opens new window) and Crane Valley Partnership (opens new window) websites.

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Page last updated: 16 Feb 2023