The problems of access control to information and technological resources of automatic control systems for water supply companies are considered. The formalized model of the process of reliable access to information and technological resources is shown. The model takes into account the existence of a multitude of communication channels and a possibility of the organization of the operative cross access. A method to ensure a reliable access to information and technical resources of automatic control systems by water supply companies on the basis of the access policy combination, a scheme of deposit and a preliminary distribution of access authenticators. As a base example there was adopted Blom’s scheme. The method allows ensuring an operative cross access in case of emergency. To ensure an operative access in the method mentioned there was used a scheme of a complete division of a secret in the combination with authenticator evolution. As a basic example the evolution of authenticators based on Lamport’s protocol is considered.