This document sets out our supplementary guidance for assessing whether customers in England and Wales: • are eligible to be supplied by a licensed water supplier (WSL); and/or • will be eligible to be provided with water and/or sewerage services by a water and sewerage licensee (such licensees are referred to as WSSLs) when the new retail market opens in April 2017. The supplementary guidance focuses on whether or not premises should be treated as household premises under section 17C of the Water Industry Act 1991 (WIA91) and so are/or will be ineligible to switch supplier. This follows requests from stakeholders such as undertakers, potential licensees, current WSLs and customer groups for additional clarity and examples following our publication of the “Guidance on assessing whether customers in England and Wales are eligible to switch their water and wastewater retailer”, which we released in August 2015 (the eligibility guidance). Ofwat has engaged with many participants as part of this process and it is vital companies determine the eligibility of premises in time for the opening of the non-household market. We consider that this guidance provides relevant participants with sufficient information to determine eligibility. Stakeholders should also note that as well as issuing the supplementary guidance, we have also updated our eligibility guidance to take into account commencement of relevant provisions of the Water Act 2014, development of our thinking on the transition from the water supply licence regime to the water and sewerage supply licence regime, and the position reflected in our supplementary guidance. Updated March 2020.