This document specifies the principles, reagents and materials, test apparatus, test methods, evaluation of results and requirements for test reports using pilot tests for industrial cooling water systems. This document specifies a method to evaluate the performance of treatment programmes for open recirculating cooling water systems. It is based primarily on laboratory testing, but the heat exchanger testing facility can also be used for on-site evaluation. This document does not include heat exchangers with cooling water on the shell-side (i.e. external to the tubes).