Dangerous water hammer pressure-transients can occur in pipelines following sudden stopping of pumps. Water column separation may occur and overpressures may damage installations. Alternative methods of alleviating the pressure fluctuations are descriptionbed and the limits of applicability of each technique suggested. Protective devices include surge tanks, discharge tanks, in-line valves and pump bypass valves for low head systems. Air vessels and release valves are most suitable for high-head pumping installations. The effect of pump inertia is explained. The paper contains a guide to the selection of the most suitable method of protection, together with design charts, equations and further references.