Salt water is one of the most aggressive liquids a pump will ever handle. Chloride ions break down the passive layer that protects ordinary 304 stainless steel, leading to pitting and crevice corrosion within months. Cast iron rusts, mild steel scales, and plastic impellers wear rapidly when sand and grit are present alongside the salt.
A true salt water pump is built differently. Wetted parts use materials that stay stable in chloride environments, seals are upgraded to silicon carbide or carbon ceramic, and fasteners are specified in a corrosion grade that matches the body. The result is a pump that keeps its efficiency and warranty intact in conditions that destroy a general-purpose unit.