Watts Premier - Reverse Osmosis Membrane with Check Valve for FMRO4-MAN, WP-5 & WP-4VThe Watts Premier Reverse Osmosis Membrane with integrated check valve is the core filtration element for FMRO4 MAN, WP 5, and WP 4V systems, removing up to 99% of contaminants down to 1 10,000 of a micron. This semi permeable membrane reduces TDS, sodium, arsenic, lead, perchlorate, chromium, copper, radium, and protozoan cysts including Giardia and Cryptosporidium. SPECIFICATIONS Membrane Performance & Ratings Filtration Rating 1 10,000 Micron