Museum conservators say that 90% of their job is controlling the flow of water. Stone sculpture and monuments suffer damage from acid rain, water-borne salts, and freezing, and some stones contain clays that expand when wet. Even within a museum, changes in relative humidity during the course of the day can cause salts to dissolve and reprecipitate, leading to stresses and cracking. We will examine some of these damage mechanisms and the methods being developed to protect against them.