In recent years steam condensate is often recovered to save energy and various water sources are used as raw water for make-up water of boilers due to shortage of water at a lot of boiler plants. In these situations the roles of deposit control and scale inhibition in boiler water become increasingly important to maintain stable and high efficient boiler system operation without energy loss nor under deposit corrosion caused by iron deposit or hardness scale adhesion.This paper investigated iron deposition and hardness scale inhibition technologies for boiler water containing high concentrations of iron up to 30 mg Fe/L or silica up to 1000 mg SiO2/L in boiler water which were some of remaining challenges in conventional technologies.As results of laboratory evaluations by using experimental boiler apparatus two iron dispersion technologies which could be selected from boiler pressure and type of make-up water were developed. One was a combination of a specific polymer and an inorganic compound and the other was use of multiple polymers simultaneously. For hardness scale control under high silica concentrations in boiler water effective polymer has specific configuration and molecular weight range. The results of several field applications of the new technologies will be also presented.