Poor injection water quality is a prime factor in the reduction in injectivity in many water injection and disposal wells. These reductions in injectivity often result in costly workovers, stimulation jobs and recompletions, or, in many cases, the uncontrolled fracturing of wells by high bottomhole pressures resulting in poor water injection conformance and reduced overall sweep efficiency and recovery. This paper discusses many commonly occurring water quality issues and how they impact injectivity, including damage due to injection of suspended solids, fines migration, clay swelling and deflocculation, formation dissolution, chemical adsorption and wettability alterations, relative permeability effects associated with the injection of skim oil or grease and the injection of entrained free gas, biologically and bacterially induced damage, formation of insoluble scales and precipitates, emulsification, wax and asphaltene deposition. Screening criteria are presented to allow for a rigorous evaluation of a particular injection water source to investigate potential areas of sensitivity and to attempt to minimize problems associated with impaired injectivity.