This document sets out our guidance for assessing whether customers in England and Wales are eligible to switch water and wastewater supplier. The Water Act 2014 (WA14) makes significant changes to the water supply licensing regime, but assessments as to the eligibility of customers to switch supplier is relevant to both the pre-WA14 regime (‘WSL’) and the post-WA14 regime (‘WSSL’), and therefore we provide guidance for both regimes within this document. Consistent with the supplementary guidance, this eligibility guidance applies to both England and Wales and to WSLs and WSSLs. The factors that are, or are not to be taken into account in determining the extent of premises will be different where the threshold limit applies. This will mean that the boundaries of premises will be more widely drawn for companies operating in accordance with a water supply licence with a restricted retail authorisation (i.e. using the supply system of an undertaker whose area is wholly or mainly in Wales. This, together with the 50 Ml/year threshold limit which has to be met in order for premises to be eligible to be supplied by a water supply licensee with a restricted retail authorisation.