Water chemistry is an important factor in the safe and reliable operation of both pressurized water reactors and boiling water reactors used to generate electric power in the United States. The chemistry parameters for normal power operation for the PWR primary water and secondary water and for the BWR reactor water and reactor feedwater/condensate are presented and discussed. Significant experiences with water chemistry and materials and operations are presented. Sources of radioisotopes that have an impact on some of the radiation concerns are listed. Water chemistry has a large impact on the economic considerations of the plants.