In California it may be best to first have a legal degree in order to understand how to collect rainwater https://legalclarity.org/california-rainwater-collection-laws-and-system-requirements/ "Navigating the permitting and compliance landscape for rainwater collection in California involves examining both state and local regulations. While the Rainwater Capture Act of 2012 allows for system installation without a water rights permit, other permits may be necessary depending on the system’s use and complexity. Systems intended for potable use could require more stringent permitting processes to ensure water safety standards are met."