New York's Appendix 5-E cybersecurity regulation for public water systems took effect March 11, 2026, making it the first mandatory, enforceable water cybersecurity framework in the country. This post covers who is in scope, what is required, when it is due, and what resources are available to help. It also examines what New York's action means in the context of a federal policy environment that is actively stepping back from sector-specific cybersecurity regulation.