Because of its lower mineral content, reverse osmosis (RO) water is often used in car washes during the final vehicle rinse to prevent water spotting on the vehicle. RO water also enables a car wash operator to reduce the demands on the vehicle drying equipment such as air blowers.
Other benefits of using RO water include less need for towel drying after the vehicle has finished the wash process and less soap required to mix with RO water because RO water has fewer minerals and total dissolved solids, thus requiring less soap to be effective.
Due to the very small pore sizes of the RO membranes it is vital that ground and surface water is adequately pre-treated prior to the reverse osmosis process. Depending on the hardness of the water involved, scaling of the filter membrane is likely to occur.
Keeping a log of the following system parameters can help you determine if scale is forming:
Water Softener is used to remove calcium and magnesium hardness from the feed water to prevent hardness scaling. This can also remove a small amount of iron.
Carbon Filter is used to remove chlorine and organics from the feed water. Free chlorine will cause rapid irreversible damage to the RO membranes. The chlorine present in most municipal water supplies will damage the thin film composite structure of the RO membranes. Carbon filtration should be used to completely remove the free chlorine residual.
A Prefilter Cartridge is used to remove smaller suspended solids and trap any particles that may be generated by the other pretreatment. The cartridge(s) should be replaced when the pressure drop across the housing increases 5-10 psig over the clean cartridge pressure drop. Typically installed on the feed water side of the reverse osmosis system, this is not considered the primary pretreatment.
When a reverse osmosis system is fed with good quality (softened, chlorine free) water, it can be trouble-free for years. In fact, RO membranes can last up to 3 years (if not longer), and a reverse osmosis system can last up to 15 years.