This report is a survey of coolant technology in water cooled reactors which focuses on the following objectives: (a) man-sievert reduction; (b) plant life extension; (c) fuel life extension; (d) general safety and materials reliability. Contents: 1. Introduction; 2. Description of reactor coolant systems; 3. Chemistry of primary coolant in water cooled reactors; 4. Corrosion in the primary coolant systems of water cooled reactors; 5. Activity transport mechanisms of water cooled reactors; 6. Decontamination of water cooled reactors; 7. Areas for future research and development; 8. Conclusions.