Implementing a chemistry programme is essential to ensure the safe operation of a nuclear power plant. It contributes to the integrity, reliability and availability of structures, systems and components (SSCs) in accordance with their intended design and functions. This revised Specific Safety Guide provides Member States with updated and more detailed guidance for the safe operation of water-cooled nuclear power plants based on current international best practices. This publication is intended for Nuclear Power Plant Chemists, Technical Support Organisations working in water chemistry and corrosion areas, and National Nuclear Safety Regulators doing oversight of NPP water chemistry programmes.