This invention relates in general to a system for treating hard water encountered in aircraft potable water equipment; such as hot water heaters and, more particularly, to the prevention of scale deposits in aircraft lavatory and galley heated water system components by installing a unique scale reduction system. The scale reduction system generally comprised of a housing with a modular cartridge inserted therein. The cartridge is porous and contains a chemical composition within its inner cavity, and this chemical composition is mixed with untreated inlet fluid flow so that the outlet flow is of a sufficiently diluted concentration. Various chemical compositions may be utilized to counteract any number of conditions that affect potable water equipment and, in one embodiment, a water softening agent is utilized to combat scale build-up in aircraft plumbing.