[en] The water chemistry of a boiling water reactor (BWR) plays an important role in several phenomena that can significantly affect both the cost of operation and the long-term viability of BWR units. Reactor chemistry was affecting operating shutdown dose rates, rad waste curie and volume generation, structural component stress corrosion cracking, and fuel performance The role of water chemistry in Zircaloy cladding corrosion phenomena are also well documented. The chemistry variables that affect these different phenomena are quite different. In some cases, the strategy to mitigate one phenomenon could potentially accelerate a negative response in another. An overall strategy to simultaneously optimize the performance of fuel, structural materials and radioisotope transport is described. This strategy, called optimum water chemistry, focuses on water purity, feed water iron levels, hydrogen water chemistry, noble metal chemical addition, and feed water zinc addition. (author)