The industry standard is to install a 5-micron sediment filter before a reverse osmosis (RO) system. The sediment filter protects the RO membrane by removing dirt, sand, rust, silt, and other suspended particles that can reduce membrane performance and shorten its service life.
Always follow the pre-filtration recommendations provided by the RO system manufacturer. While most systems specify a 5-micron sediment filter, some manufacturers may require a finer 1-micron cartridge depending on the design of the system. Failure to follow the manufacturer's recommendations may affect system performance and could void the warranty. Always review the manufacturer's installation and warranty requirements before selecting a pre-filter.
Proper Filter Sizing
Be sure to select a filter cartridge that is large enough to provide the required flow rate without causing excessive pressure loss. As a general guideline, the filter should have a clean flow rate capacity of at least twice the desired system flow. Depending on the water quality, a flow capacity of 1.5 times may be adequate for light sediment conditions, while up to 3 times may be recommended for heavy sediment loads. The goal is to have a sediment cartridge last between 4 and 6 months before a change out is required. If a cartridge with too low a flow capacity, more frequent change outs may be required.
Heavy Sediment Applications
If your water contains large amounts of sand, grit, or other visible sediment, installing an additional coarse pre-filter ahead of the 5-micron sediment filter is recommended. This first-stage filter removes larger debris and helps extend the life of the finer sediment filter and the RO membrane.
Typical Pre-Filtration Layouts
Municipal / City Water
Municipal water supplies generally contain very little coarse sediment. In most applications, a single 5-micron Point-of-Entry (POE) sediment filter installed before the RO system provides adequate protection. Always verify the required micron rating with the RO system manufacturer.
Well Water
Well water often benefits from a two-stage pre-filtration system to prevent the finer sediment filter from plugging prematurely while maintaining good water pressure.
CAUTION: If selecting a carbon filter for use with a water well system, never use an activated carbon filter that uses any cellulose material in it’s construction. A carbon block or granular carbon type filter is recommended.
To better understand the pro’s and con’s, please click here.
First Stage
Option 1: Install a traditional whole house sediment filter with a coarse 30 to 50-micron cartridge. A washable pleated polyester cartridge is a good reusable option, while spun polypropylene cartridges provide an economical disposable solution.
Option 2: Install a Spin-Out filter to remove coarse sand and larger particles. Keep in mind that even the finest 1000-mesh Spin-Out filter only removes particles down to approximately 15 microns, so it does not provide sufficient protection for an RO membrane on its own.
Second Stage
Install an activated carbon filter immediately before the RO system. The carbon removes chlorine, chloramine and volatile organic compounds (VOC’s), providing the level of protection needed for the RO membrane.
Post-Filtration (Polishing)
After the water leaves the RO storage tank, the water typically passes through a final post-filter (a second activated carbon filter) which is installed in line before the RO water reaches the drinking water faucet. The purpose is to remove any remaining tastes or odors from the treated RO water. This final stage of treatment is commonly referred to as polishing, as it improves the taste and odor of the product water before it is dispensed.
CAUTION: If selecting a carbon filter for use with a water well system, never use an activated carbon filter that uses any cellulose material in it’s construction. A carbon block or granular carbon type filter is recommended.
To better understand the pro’s and con’s, please click here.