Water audit validation is the process of examining water audit inputs to improve the water audit’s accuracy and document the uncertainty associated with water audit data. This project developed guidance on Level 1 water audit validation using version 6 of the American Water Works Association (AWWA) Free Water Audit Software. It highlights the factors that influence water audit data quality and the key points to consider when assessing whether the correct methodology was used to derive audit input values. The project is an update to project 4639, Level 1 Water Audit Validation, which provided guidance for those using version 5 of the AWWA Free Water Audit Software. Published in 2021.