Guidelines for Acceptable RO Feed Water

Feed water to reverse osmosis (RO) systems should have guidelines established for quality control purposes. Problems such as scaling, fouling and degradation of filter membranes arise if feed water is not pretreated. A water quality test on feed water ensures prevention of these problems.

Considerations of Nutrients

• Hard water deposits caused by high calcium and magnesium in feed water can cause scaling in RO systems. This can be prevented through acidification by adding sulfuric or hydrochloric acid to the feed water, which prevents crystallization of calcium and magnesium. Adding a water softener agent, such as lime or sodium hydroxide, can also prevent scaling through ion exchange.

Microbes and Mineralization Effects

• Microbes, minerals and organic matter can reduce the performance of RO systems. Feed water should be chlorinated in order to kill any microbial organisms. Using chemical treatments, such as a cationic polymer (used in pool supplies), to enhance coagulation of minerals and solids followed by filtration will greatly expand the life span of RO systems.

pH and Oxidizer Problems

• Highly acidic or alkaline feed water can destroy a RO membrane quickly. pH of feed water should be between 6.5 and 8.5, although 8 to 8.5 is best. This is achieved by acidifying or adding a basic agent to lower or raise the pH. Additionally, high oxidizers, such as chlorine, promote the ruin of membranes and need to be used cautiously.