This document provides guidance for establishing whether business customers in England and Wales are eligible to switch the water and sewerage retailer serving their premises. It includes both statutory and non-statutory guidance. Since the business retail market opened in April 2017, eligible business customers in England have been able to choose their supplier of water and sewerage retail services. There is no threshold requirement in terms of water consumption. In Wales, business customers are only able to switch their water retailer and to be eligible their water consumption has to meet a 50 megalitres (ML) per year threshold requirement. In July 2016, we issued guidance on eligibility alongside supplementary guidance following requests from stakeholders for additional clarity and examples. In March 2020, we reissued our guidance, and supplementary guidance to confirm that from 1 April 2020, our guidance would apply in the Isles of Scilly. This current version of the guidance combines, and updates, the two guidance documents we issued in March 2020. Part A is applicable in England whereas Part B is applicable in Wales.