Recent Trends in inhibitors are reviewed from the viewpoint of comparing inhibitor costs estimated by the Uhlig method in 1997 with that in 1995. The increase of inhibitor costs in boiler water and industrial cooling water is almost equal to the growth of Gross National Product (GNP). On the other hand, the cost of water treatment for air conditioning goes right on increasing. In the last three decades two main developments in inhibitor technologies had been accomplished. One is less toxic corrosion inhibitors such like phosphonates, zinc, polymers and natural materials instead of chromate and hydrazine. Another is polymeric dispersants for increasing the reuse of water. The demand for environmentally friendly corrosion and scale inhibitors, so called green inhibitors will accelerate the development of inhibitors that are more environmentally acceptable and cost-effective. Non-chemical water treatment combined with several processes such like deaeration, filtration, ion-exchange, reverse osmosis and so on will be also developed at the next decade.
