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Trade effluent charges

We calculate trade effluent charges based on the volume and strength of the discharge. We pass these charges to your retailer, who will then pass them on to you.

A circular clarifier at the Peel Common Wastewater Treatment Works on a sunny day

How am I charged?

Since the opening of the retail market in April 2017, non-household customers are now billed by their chosen retailer rather than wholesalers like Southern Water.

We are still responsible for managing trade effluent discharges into our network and for setting up trade effluent accounts for billing. If you have any queries about your bill or charges, please contact your retailer. 

Frequently asked questions 

Here are answers to some commonly asked questions about trade effluent charges.

Your retailer will provide your billing services, not Southern Water.

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

You will often be charged based on the volume and the strength of the trade effluent discharged. Charges may be calculated using the Mogden formula. This considers the difference between your trade effluent and 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 need to transport, treat and dispose of the effluent.

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

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

By reference to, but not limited to:

  • Meters that are sub-meters to a main meter
  • The estimated volume where Southern Water determines that a meter reading may not be suitable for the purposes of calculating charges. This may be 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

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 assessing the strength of a trade effluent discharge for billing purposes. In such cases, the company will agree with the customer and their retailer on 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-month rolling average
  • A three-month rolling average
  • A one-month average

Your retailer will bill all trade effluent services apart from the non-standard charges below. Southern Water will charge you directly for these and you'll 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. This will be in case we anticipate a breach or breach 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)



£296.00 per sample

Formal sampling charge (6pm - 7am)



£554.00 per sample


Need more support?

We're here to help if you have any other questions. Please fill out this form in as much detail as possible to help us answer your query.

Repaired a leak

This can be found in the top right corner of your bill and is 8 or 10 digits long.

This is the reference on the back of the leaflet that one of our members of staff left with you