Controlled release coolant additive composition

The present invention relates to a controlled-release additive composition for use in water treatment systems, particularly coolant and hot water systems, for example, engine coolant systems, and to a method of using said additive compositions. The controlled release additive composition comprises a water-soluble core containing at least one water treatment chemical and a polymeric coating material encapsulating said core which slowly releases the water treatment chemical into the water treatment system, thereby delivering an effective level of the water treatment chemical to the water treatment system over an extended period. A controlled-release coolant additive composition for use in engine coolant systems comprising a core containing at least one coolant additive component and a polymeric coating encapsulating said core. The controlled released coolant additive composition slowly releases the coolant additive components to an engine coolant system, thereby delivering an effective concentration level of coolant additive components over an extended period. The controlled-release coolant additive composition maintains a minimum concentration level of active coolant additive components in the coolant system.