Purified water is one of the most important resources you’ll find in the lab. Reagent grade water systems allow labs to take tap water, or in some cases pretreated water, and convert it into a purified form, suitable for making reagents. Purified water is classified by its resistivity, conductivity, and total organic content, breaking it down into type I, II, and III water systems. Type II water is suitable for use in most reagents. Some factors to consider in purchasing a reagent grade water system include the instrument’s footprint, its monitoring capabilities, maximum output, and feed source.