Businesses Trade effluent

Trade effluent is any liquid waste (effluent) discharged into our sewers from a business or industrial process on a trade premises.

For non-household customers, your retailer should be your first point of contact. For more information on how to choose your retailer, please visit the Open Water website.


Understanding trade effluent

What is trade effluent?

Trade effluent is any liquid waste (effluent) discharged into our sewers from a business or industrial process on a trade premises.

This includes any wastewater derived from a production process or from washing down or cooling activities, including wastes from public-funded activities such as municipal landfills.

This can be best described as anything other than domestic sewage (toilet, bath or sink waste) or uncontaminated surface water and roof drainage (rainwater).

Section 141 of the Water Industry Act 1991 defines trade effluent as: 'any liquid, either with or without particles of matter in suspension in the liquid, which is wholly or partly produced in the course of any trade or industry carried on at a trade premises.'

Trade effluent includes wastewater coming from, but not limited to:

  • Commercial car wash
  • Laundries/launderettes
  • Food and drink production
  • Chemical manufacturers

The following activities are currently not consented under trade effluent legislation and you may follow specific guidance for the disposal of waste into our sewers:

  • Kitchens and toilets at commercial premises
  • Hairdressers
  • Swimming pools (domestic)
  • Offices and non-household premises that only discharge domestic sewage
  • Restaurants, pubs, hotels, takeaways, canteens and healthcare sector meal services (we expect these activities to have suitable grease management procedures in place as well as measures to prevent food waste from entering the public sewer)
  • Hospitals, nursing/care homes, GP surgeries, dental practices and veterinary practises

If you have any enquiries related to the above, please get in touch with the Trade Effluent team using the details below.

Why does Southern Water need to control trade effluent?

Unlike domestic sewage, trade effluent is highly variable in terms on strength and volume and may contain substances that present the risk of harm to people, our sewerage network, treatment processes and the environment. 

Trade effluent controls are in place to reduce these risks to acceptable levels and ensure that our network and treatment processes are not overloaded, which could have a potential detrimental and catastrophic impact on the receiving environment.

Under Section 111 of the Water Industry Act 1991, it is an offence to discharge any matter likely to injure the sewer or drain, to interfere with the free flow of its contents or to affect prejudicially the treatment and disposal of its contents.

What happens to your trade effluent in the water cycle?

Trade effluent discharged to our sewers is mixed with domestic sewage and directed via pump or gravity to one of our water recycling centres.

The incoming wastewater passes through a screen where large solids are removed. Then the wastewater is put through a settlement process. Here, heavy particles of solid waste sink to the bottom of a tank to form a layer of sludge. The sludge recovered goes to a sludge treatment centre for further treatment, including digestion to remove harmful bacteria allowing it to be recycled to land (farmers can use it as fertilisers).

The next stage (biological treatment) uses bacteria and microbes to remove organic contaminants from wastewater. The naturally occurring biomass breaks down the organic material as food and converts it into less harmful components.

Finally, the almost clean water goes through an additional settlement stage (clarification), which removes any remaining waste particles. In some cases further treatment is required to meet stricter limits, where, for example, we discharge into nutrient-sensitive watercourses or bathing waters. The treated final effluent is eventually discharged back into the environment where it is ready to go through the cycle all over again.

Infographic: What happens to your Trade Effluent in the water cycle


What is the water retail market?

Since 1 April 2017, the business retail water market is open to businesses, charities and public sector organisations with premises that qualify.

These ‘non-household’ customers are likely to be eligible if their premises are:

  • used mainly for business
  • supplied from a wholly or mainly English-based water company.

Licensed retailers now buy wholesale water services – the physical supply of water and the removal of wastewater – from the regional water companies, who continue to supply your water, treat your wastewater and maintain the water and wastewater pipe networks.

The retailers package these water services with other services and compete for customers.

Infographic: The water retail market

Customers are free to choose their retailer by looking at who has the best deal for them. If you don’t have a retailer yet, you can find a retailer now.

Every business premises has a unique Supply Point Identifier (SPID number) to identify the water and/or sewerage supplies at the property. You can find a copy of your water and sewerage SPID on your bills. Otherwise, you can obtain your SPID by contacting your retailer and providing your premises address.

In some cases, you may not have a SPID and a SPID will be specifically created for your site on issuing of a trade effluent consent.

Can I discharge trade effluent to a surface water sewer?

No. Trade Effluent should only be discharged to a foul or combined sewer.

A surface water sewer should only collect uncontaminated rainwater run-off as it goes directly into a watercourse. Discharging wastewater, such as sewage and trade effluent, into a surface water sewer can cause serious environmental pollution.

Does Southern Water have a right of access onto my site?

Yes. We have the right to enter your site at any reasonable time to take a sample of your trade effluent.

Under Section 171 of the Water Industry Act 1991, any person designated by a sewerage undertaker shall have a right to enter any premises at all reasonable hours for the purpose of taking action or carrying out any works (i.e. collection of trade effluent samples or enforcement action when Southern Water believes a discharge is harming our assets or the environment).

How do I temporarily discontinue my trade effluent services?

If your company temporarily ceases its operations or temporarily stops discharging trade effluent, you should notify your retailer. Following agreement by Southern Water and the retailer, the consent can be put on a discontinuation status. The trade effluent charges payable for the agreed duration of the discontinuation shall be trade effluent standing charges only (no volumetric charges).

Discontinuation of the trade effluent consent will apply from the first day of the following month.


Will Southern Water take samples of my trade effluent?

Yes. We routinely inspect and sample trade effluent discharges in order to:

  • check compliance against consent conditions
  • determine the volume and strength of the effluent for charging purposes
  • assess the volumes and strengths of trade effluent being discharged to see what effect they have on our assets.

For any samples taken by Southern Water, you will receive correspondence by email confirming your sample results. If you wish to receive the original analysis certificate from the laboratory, you will need to notify your retailer (certificate issue will be subject to an annual charge). All sample analysis will also be provided to your retailer.

How often will Southern Water visit and take samples?

For each trade effluent consent, the number of samples Southern Water will strive to take in each year will be determined by the risk assigned to the trade effluent discharge

Factors considered when calculating the risk of a trade effluent discharge:

  • Consented suspended solids limit
  • Processes generation the trade effluent
  • Capacity of the receiving treatment works
  • Maximum permitted volume to be discharged (m3/day)
  • Compliance history
  • Presence of priority or/and accumulative substance
  • Consented chemical oxygen demand (COD) limit

The samples can vary from zero to 48 samples per year depending on the value of the consent monitoring risk associated to the discharge. 

Infographic: Factors considered when calculating the risk of a trade effluent discharge

Do I need to provide a sampling point?

Yes. As part of a consent, a trader is required to provide a sampling point so that samples of trade effluent can be given for control and charging purposes.

The sample point must be such that it will provide a sample of the trade effluent discharged to the public sewer without domestic sewage contamination, and provide safe and reasonable access at all times.

Water Industry Act 1991, section 121: Conditions of the consent – ‘the provision and maintenance of such an inspection chamber or manhole as will enable a person readily to take samples, at any time, of what is passing into the sewer from the trade premises’.

Can customer samples be used for monitoring and billing purposes?

Yes. The company may use sample analysis provided by the retailer or its customer for the purposes of consent monitoring or calculating trade effluent charges by agreement with the retailer. All such sample analysis must be carried out by a UKAS accredited laboratory and be taken from the previously agreed sample point. 

Do I need to self-monitor the trade effluent?

Self-monitoring requirements may be incorporated into trade effluent consents.

Customers are encouraged to set up self-monitoring programmes as they assist with the early detection of problems.

Who is responsible for the health and safety of Southern Water staff on my site?

Both the occupier of the premises and Southern Water have a duty under the Health and Safety at Work etc. Act 1974 to ensure that any visiting Southern Water employees can safely carry out their duties.

Our employees shall act with due care for their own health and safety and observe any site specific health and safety arrangements.


How am I charged?

Your billing services are provided by your retailer and not by Southern Water.

Since the opening of the retail market in April 2017, all non-household customers are now billed by their chosen retailer. Wholesalers, like Southern Water, are still responsible for managing trade effluent discharges into their network and for setting up trade effluent accounts for billing, but they will charge your retailer who then charges you, their customer.

For queries about your bill or charges, please contact your retailer. Your retailer may be able to advise you on how to save water, spend less and get other benefits.

Trade effluent customers will often be charged on the volume and the strength of the trade effluent discharged. Charges may be calculated using the Mogden formula which considers the difference of your trade effluent to average domestic sewage with regard to chemical oxygen demand, solids and, in some cases, ammonia. High concentrations of these parameters are likely to cause higher bills due to the requirement to transport, treat and dispose of the effluent.

How is the volume calculated for charging purposes?

The volume of the trade effluent taken as having been discharged shall, for billing purposes, be the volume:

  1. Recorded on a meter installed on the effluent discharge pipe
  2. Assessed from the volume of water supplied recorded on a meter or meters installed on the water supply
  3. Calculated by Southern Water

By reference to, but not limited to:

  • Meters that are sub-meters to a main meter
  • Estimated volume where Southern Water determines that a reading on a meter may not be suitable for the purposes of calculating charges due to an occurrence such as, leaks or mechanical failure of the meter 
  • Standard allowances
  • Customer-specific allowances determined by Southern Water
  • Rainfall
  • Conceited volume

How is the effluent strength calculated for charging purposes?

Calculation of a representative COD settles, suspended solids pH7 and ammonia concentrations.

1. Standard strength

For specific types of discharge, a standard strength will be used to calculate the unit charge. These strengths are fixed by the company for each charging year and are based on its analysis of the particular type of discharge.

2. Agreed strength

The company may decide that the standard sampling is not appropriate for determining the strength of a trade effluent discharge for billing purposes. In such cases, the company will agree with the customer and their retailer an appropriate agreed strength.

3. Actual strength

The calculation of COD settled, suspended solids pH7 and ammonia for billing purposes will be calculated by one of the following:

  • A 12 moth rolling average
  • A three month rolling average
  • A one month average.

What does Southern Water charge for?

All trade effluent services will be billed through your retailer apart from the non-standard charges below. Southern Water will charge you directly for the non-standard charges below and you will receive these invoices separately.


Recovery of incurred costs

  • The recovery of extraordinary costs incurred by Southern Water due to an event caused by you. This includes, but is not limited to, damage to our assets or increased operational costs.
  • The recovery of costs incurred by Southern Water in respect of pre-emptive measures undertaken by us to minimise the impact on our assets in anticipation of a breach or breaches of your trade effluent consent.


Formal sampling charge

The recovery of costs incurred by Southern Water in respect of formal sampling undertaken in accordance with our policies and procedures, due to the failure to comply with your consent.







Recovery of incurred costs



Determined on an individual incident basis

Formal sampling charge (7am - 6pm)



£255.00 per sample

Formal sampling charge (6pm - 7am)



£480.00 per sample




Who takes my meter readings?

When Southern Water owns the meter, it is responsible for the meter maintenance and set up, including the initial and final meter reads. The retailer is then responsible for all the meter readings on a regular cyclic basis. Private meter maintenance and installation is the responsibility of the customer – reads should be provided regularly to the retailer to input for billing purposes and the wholesaler for compliance and monitoring. Any changes to your private meter should be reported to your retailer as soon as possible.

How do I get a private trade effluent meter installed?

You can get a private trade effluent meter installed to improve the accuracy of the trade effluent volume calculation for both monitoring and charging purposes. You are responsible for installing and maintaining the equipment. If you're installing a new meter, replacing an existing meter or think you might have a faulty private meter, please contact your retailer.

Contact us

If you've any questions regarding trade effluent, contact us using any of the methods below.

For all general trade effluent enquiries or complaints, please contact your retailer in the first instance.

If you have a specific trade effluent consent query, you can contact your Trade Effluent Inspector or email: [email protected].

For any historic billing queries or complaints (before 1 April 2017), contact our Transition team: [email protected].