Because your library IS an Online Service Provider, and because your library has a commitment to patron privacy, you should read the EFF guide to Best Practices for Online Service Providers.
“OSP owners must deal with requests from law enforcement and lawyers to hand over private user information and logs. Yet, compliance with these demands takes away from an OSP’s goal of providing users with reliable, secure network services. In this paper, EFF offers some suggestions, both legal and technical, for best practices that balance the needs of OSPs and their users’ privacy and civil liberties.”