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Trade effluent

Trade effluent is any liquid waste that’s discharged into our sewers from a business, industrial or trade process, excluding domestic sewage and surface water.

Why do we need to control trade effluent?

As part of the Water Industry Act 1991 we have a legal obligation to control trade effluent. Trade effluent is highly variable in volume and strength, and controlling it helps us to:

  • Protect the health and safety of the public and our workers
  • Preserve our environment and maintain drinking water quality
  • Protect our valuable sewer network and assets

What is a trade effluent consent?

If you want to discharge Trade Effluent into a public sewer, you’ll need permission from us before you can do so - this is granted with a consent. A trade effluent consent is a legal document issued under the provisions of the Water Industry Act 1991. It’s an offence to discharge trade effluent without a consent.

The consent will contain conditions and limits to the discharge. Breaches of any consent condition constitutes a criminal offence under the above Act and may lead to legal action being taken against the discharger.

Legal action will be considered in all cases, particularly where a serious, severe, persistent and or blatant breach of the relevant legislation has taken place.

Conditions are determined on an individual basis, but limits we usually consent for include:

  • Volume/flow rate: This is limited by the maximum daily amount (m3/24hr) and litres/second of trade effluent you’ll be able to discharge. The volume and flow rate can be limited and assessed on an individual basis.
  • Suspended Solids: Suspended solids can cause siltation and blockages in the sewerage system.
  • Oil and Grease: Oil and grease can build up within the sewer which can lead to blockages, odour problems and subsequent flooding. Oil and grease can also build up in our equipment and cause operational issues.
  • Ammonia: Ammonia can cause unsafe sewer atmospheres and can also causes toxicity issues within a watercourse as ammonia is highly toxic to aquatic animals.
  • pH: The normal range of pH allowed is 6 to 11. It is a measurement which tells us how acidic or alkaline the discharge is. Extremes in pH can damage our sewer network or make it dangerous for our staff.
  • Temperature: Extreme temperatures can lead to unsafe working conditions for our staff. Up to 43.3 degrees Celsius is our standard temperature limit.
  • Chemical Oxygen Demand Limit: COD is a measurement that tells us the quality of the water and is controlled to ensure we don’t overwhelm our biological treatment processes.

Who should apply for a trade effluent consent?

This table outlines example industry types that would normally require a consent to discharge trade effluent. This is only a guideline and each customer will be assessed on an individual basis.


Industries that would normally require a consent  Industries that would not normally require a consent 
  • Launderettes
  • Commercial car wash
  • Food and drink production
  • Commercial swimming pool
  • Metal finishers
  • Engineering/chemical production
  • Landfill leachate and waste/recycling centres
  • Construction works
  • Non-household premises/offices that are only discharging domestic waste
  • Toilets at commercial premises
  • Domestic swimming pools
  • Takeaways, pubs, restaurants, canteens and hotels
  • Hairdressers


We also issue consents for temporary trade effluent discharges (6 months or less). Examples of this could include:

  • Groundwater from construction
  • Heating system flushing
  • Shorter term construction works

What happens after a consent is issued?

When a consent is issued, we’ll send it to the person who applied for the consent at the premises address. In the case of a partnership or private business we’ll send it to the named partners/owners at the business or private address. We may carry out sampling and analysis to work out the appropriate charging methodology.

We can’t provide specific trade effluent technical advice. However, your retailer may be able to advise you, and there are specialist companies available to help.

From time to time, we’ll make a visit to monitor compliance against consent conditions. We may need to take samples and read meters to assess the effluent and manage health and safety risks. If any samples taken aren’t compliant with the consent, charges may be applied, and legal action may be taken.

Thames Water staff have legal right of access to monitor and carry out enforcement activities. They should carry identification on them, and you can also confirm their identity by calling our Trade Effluent department.

If you disagree with the conditions of your consent, you have a right to appeal.

Trade effluent should never be discharged to a surface water sewer, and it can only be discharged to a foul or combined sewer with a consent in place. If you’d like to discharge direct to a watercourse, please contact the Environment Agency.

If you’re aware of an illegal discharge, please contact our Trade Effluent Team immediately on 0203 577 9200. If a spillage or incident needs immediate action, please call 0800 009 3931.

Managing your application

Trade effluent applications must be made using the Trade Effluent Customer application form on the MOSL website. You can find the form in the Code Defined Documents section under Customer Forms.

This can be done via your wastewater retailer.

When we receive your application, we’ll assess it. We may need to get in touch with you and/or your retailer to check the details and carry out a site visit. 

We do our best to fairly assess all trade effluent applications. In some circumstances we may need to reject applications where we haven’t received enough information, or the discharge is too high risk. 

If a trade effluent discharge can’t be accepted into our sewer network, alternative waste disposal methods may be needed, such as tankering by a licensed waste disposal company. 

If your circumstances change or you’re no longer discharging, you may be required to submit a variation to an existing consent or request a termination of your consent. Please contact your retailer for advice. 

Consent register

We’re required by law to share a public register of all trade effluent consents we have authorised. Please contact us if you require copies of any consents.

Contact us

Thames Water Trade Effluent Department
Trade Effluent Team
Lovick House
Crossness STW
Bazalgette Way
Abbey Wood

Telephone: 0203 577 9200