Corrosion, a complex electrochemical phenomenon that cannot always be eliminated but can usually be controlled in a cost-effective manner, may be uniform and attack a surface evenly or may cause severe localized problems such as a crevice or pit. For the corrosion reaction to proceed, all components of an electrochemical cell--an anode, a cathode, a connection between the anode and cathode, and a conducting solution--are required. Methods for documenting corrosion range from simple visual inspections to complex scale analyses. Laboratory and pilot tests can be used to define the extent and magnitude of corrosion. Corrosion control programs should be developed with a two-phased approach in mind: changing water chemistry and using corrosion resistant materials.