Building and Developing

New site developments
If you're building multiple domestic or commercial properties on a site that will have a new road/access you'll probably need a new water main. You can choose either STW or a WIRS accredited Self Lay Provider (SLP) to lay the new main and/or service connections. Proposed sewers into the site can be offered to us for adoption so we become responsible for them.

New Appointments and Variations (NAV)

What is a NAV?

Under the Water Industry Act 1991, water companies operating the public water and / or wastewater networks hold an “Instrument of appointment”, allowing them to provide water and/or sewerage services to customers in a defined geographical area.   A NAV (New Appointment and Variations) involves one company replacing another as the appointee for an area.  NAV companies are therefore limited companies which provide a water and/or sewerage service to customers in an area which was previously provided by the incumbent monopoly provider.

There are three circumstances in which a NAV can be granted:

  • Where the premises of one or more customers is supplied (or is likely to be supplied) with at least 50 megalitres of water per year. The same criterion applies for water recycling services.
  • Where no premises within the area are served by an appointed company i.e. the site is ‘unserved’. This includes areas which are supplied by private, unregulated supplies. This criterion must be met for both water and water recycling services.
  • If the existing appointed company consents to the transfer of that area.

A new appointment is made when a limited company is appointed by Ofwat for the first time to provide water and/or sewerage services for a specific geographical area.  A variation is where an existing appointed company asks Ofwat to vary its appointment so it can extend the area it provides services to. A new appointee has the same duties and responsibilities as the previous statutory water company.

For further information, see how Ofwat govern the NAV application process.

Services to NAVs

If you are a NAV company seeking to become the appointee for a site that’s currently in our area, you will need some information from us as the incumbent water and/or wastewater company to support your application to Ofwat. This may include confirmation of whether we serve properties within the site, setting up a bulk agreement and providing bulk connections for water and/or wastewater to the boundary of your site. 

Requesting a copy of our water and sewer network plan

Before you start any development work you can request an instant download of our existing mains and sewerage network plans to check that your site is within the Severn Trent Water boundary. Charges apply. 

Alternatively, you can view our maps free of charge, by appointment only by visiting the Severn Trent Centre at: 2 St John's Street Coventry CV1 2LZ.  Further details of these services can be found in our New Connections Scheme of charges.

Site served assessment

If you need confirmation of the served status of a site, to support your application under the “unserved” criteria, please send us a plan showing the site boundary on an OS background, stating the services requiring assessment (i.e. water, wastewater, surface water). On brownfield development sites, if there are existing premises within the proposed NAV boundary, please provide any available details of the bill recipient and disconnection plans.  Enquiries should be sent to  We will undertake a check of our records and respond within 21 days. No charges apply.

Point of connection / Point of discharge enquiries

If you need to understand the requirements for supplying your new site with bulk water and /or sewerage connections, you can send us a NAV development enquiry before making a full application. We’ll complete an assessment to understand the impact of the proposed development on our water and/or sewer network and provide a response outlining the budget cost of providing a bulk connection to your site,  capacity availability and constraints, indicative information on any reinforcement works (if required) and details of infrastructure charges, credits and income offset applicable to your site. We will provide a response within 28 days. Application fees apply to this enquiry.  See our New Connections Scheme of charges.

You can submit a NAV development enquiry online using the application button below.

Bulk agreements

If we are providing bulk water and/or wastewater connections to supply your site, we’ll need to enter into a Bulk Supply and / or Bulk Discharge Agreement. Ofwat will require this agreement to be in place before they grant the appointment or variation. You can request bulk agreements by emailing us at Unless advised otherwise, we will use details and drawings provided as part of your enquiry and site served assessment to compile the agreement(s). No charges apply.

Bulk water connection applications

When you are ready for your bulk water connection you will need to make a separate mains application to obtain a NAV offer letter containing a design and firm quotation for the offsite works required to provide the bulk water connection to your boundary. Mains application fees apply. You will need to pay the connection costs in full before we proceed with the works.   Please email for further details.

Bulk discharge connection applications

Our response to your initial point of discharge enquiry will identify a suitable point of discharge for your site. When you are ready to make your bulk sewer connection to our network you will need to apply for approval to connect using the S106 sewer connection application process. Application and inspection fees apply. 

Details of charges applicable to NAVs for enquiries and applications for bulk water and wastewater connections can be found in our New Connections charging scheme. Application fees and charges for NAVs are the same as those for other customers such as developers and self lay providers, seeking equivalent services.    

Details of the tariffs applicable to NAVs for bulk supplies and bulk discharges can be found in our Wholesale Scheme of charges and in the NAV Charge document and Cost Model below.