Large selection of replacement water filters, reverse osmosis membranes, testing kits and water filter system repair parts. From one water filter or membrane to case quantity discounts.

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WaterFiltersOnline.com 4 Stage Reverse Osmosis RO System Water Filters

WaterFiltersOnline.com 4 Stage Reverse Osmosis RO System Water Filters

WaterFiltersOnline.com 4 Stage Reverse Osmosis RO System Replacement Water Filters And Reverse Osmosis Membranes. All service parts in stock.
  1. GE Osmonics ® Purtrex PX-5-978 Sediment Replacement Water Filter # 93023
    GE Osmonics ® Purtrex PX-5-978 Sediment Water Filter # 93023
    GE Osmonics ® Purtrex PX-5-978 5 Micron Sediment Water Pre Filter. True-graded density pure polypropylene depth replacement water filter. # 93023 9 7/8" long X 2 1/2" diameter. 40 per case, sold individually. Order a case and save even more. Learn More
    $8.99 Special Price $5.99 As low as $3.99
  2. Pro Products Sani System Sanitizer
    Pro Products Sani System Sanitizer
    Pro Products Sani System Sanitizer. 0.25 or 0.5 fl. oz. concentrate. Sani-System ® Pro Products is proud to introduce Sani-System, the first and only EPA product approved for sanitizing water softeners, RO units and Water Coolers. Sani System is proven to kill 99.9% of E. coli, E. coli O157:H7, Staphylococcus aureus, Listeria monocytogenes and other harmful bacteria. It does not use chlorine, other oxidizers or acids that can harm water softener equipment parts. Use is simple; each dose comes in a pre-measured pouch. Just cut, pour and regenerate softener. No measuring, No mess! Sanitizing Equipment! Applications Interior Surfaces of Water Softeners, Reverse Osmosis (RO) Units, Ice Machines, Water Coolers, Water Holding Tanks and Pressure Tanks. Sani-System is now NSF certified! This is the best sanitizing solution available anywhere! Stock up and save. Learn More
    $7.99 Special Price $4.99 As low as $2.49
  3. TDS Meter - Test For Total Dissolved Solids In Water - Reverse Osmosis Membrane Tester - TDS Meter
    TDS Meter - Test For Total Dissolved Solids In Water - Reverse Osmosis Membrane Tester - TDS Meter
    TDS Meter - Tester. The Only Way To Know If Your Reverse Osmosis RO Membrane Is Performing Correctly - Tests for TDS - Total Dissolved Solids. A Must For All RO System Owners. Compare Incoming Feed Water To Treated Water - Replace Membrane If Less Than 80% of TDS Is Being Removed - The lower the TDS level in the water, the more efficiently your body's cells actually get hydrated by the water that you drink. The higher the TDS levels in the water, the greater the probability of harmful contaminants that can pose health risks or hinder the absorption of water molecules on the cellular level. Simple to use for Reverse Osmosis membrane monitoring. We really like this tester and think that anyone who wants to know about the quality of their water should have one of these TDS Meter Testers to monitor their RO membrane. Learn More
    $49.99 Special Price $37.99 As low as $17.99
  4. TDS Meter Inline Water Tester DM1 - HM Digital Dual Mode Reading
    TDS Meter Inline Tester- Dual Mode Reading - Easily Installs Inline - Very Simple To Use
    TDS Meter - Dual Mode - Installs Inline - Check the TDS level with the push of a button. Now you can easily check to make sure the water from your reverse osmosis system is top quality. Measure the tap water coming in vs. the purified water going out of your system at any time. Very easy installation. FEATURES Displays TDS levels of the feed water and product water with in & out electrode probes. Highly efficient and accurate due to its advanced microprocessor technology. Auto-Off function conserves battery power. The unit shuts off automatically after 10 minutes of non-use. Comes equipped with John Guest Quick-Connect T-fittings as shown. Installs quickly and easily. SPECIFICATIONS Range: 0-9990 ppm Accuracy: ±2% Always know if your RO membrane is performing correctly! Learn More
    $49.99 Special Price $39.99 As low as $19.99
  5. DOW FILMTEC -  TW30-1812-50 RO Reverse Osmosis Membrane #80722-1000
    Dow Filmtec ® TW30-1812-50 RO reverse osmosis membrane # 80722
    Dow Filmtec ® TW30-1812-50 TFC 50 GPD RO reverse osmosis membrane - standard size 1.75" X 11.75" Part # 80722 Learn How To Upgrade Your Reverse Osmosis Membrane Capacity Learn More
    $84.99 Special Price $69.99 As low as $54.99
  6. Molykote-From DOw Corning- 111 Compound-6 Gram O-ring Silicone Lubricant & Sealant-Dow-111-5-gram-1000
    Dow Corning (Molykote) ® 111 6 gram O-ring Silicone Lubricant and Sealant - Be sure to lube your O-rings to help prevent leaks.
    Dow Corning/Molykote ® 111 6 gram O-ring Silicone Lubricant and Sealant - 6 gram pillow pack. (like a ketchup packet) Great O-ring sealant and lubricant. FDA and NSF approved. (Do Not Use Petroleum Jelly As It May Break Down O-rings Or Housings) This is the same premium grade silicone sealant and lubricant used in underwater photography cameras, scuba gear and other underwater applications that simply can't afford leaks. Why not use the best for your reverse osmosis or drinking water filtration system?

    Dow 111 Silicone MSDS Safety Sheet

    Learn More
    $5.99 Special Price $3.99 As low as $1.79
  7. Replacement Non-Air Gap Pure Water Faucet For Water Filter Systems
    Replacement Non-Air Gap Pure Water Faucet - Calif. Low Lead Level
    Replacement Non-Air Gap Pure Water Faucet - Calif. Low Lead Level. Has one single tube connection. 7" high. Long reach - Extends 5 1/2" from center of faucet. Learn More
    $34.99 Special Price $19.99 As low as $14.99
  8. Omnipure CL-10RO-T/33 GAC Inline Replacement Water Filter-1000
    Omnipure ® CL-10RO-T/33 GAC Inline Water Filter
    Omnipure ® CL-10RO-T/33 GAC - 10" X 2" Carbon Inline Replacement Post Water Filter - GAC (granular activated carbon) Acid Washed Carbon - Should be changed at least every 12 months. 25 per case, sold individually. Order a case and save even more. Learn More
    $21.99 Special Price $11.99 As low as $9.49
  9. Standard Four Stage RO Reverse Osmosis Water Filter Change Kit- 1000
    Four Stage Standard RO Water Filter Change Kit
    Four Stage Standard RO Reverse Osmosis Water Filter Change Kit. One Year Filter Change Kit: (2) 5 Micron Poly Spun Sediment Pre Filters (9 7/8") (1) 10 Micron Extruded Carbon Pre Filter (9 3/4") (1) In-Line GAC Post Filter (Granular Activated Carbon 10") The sediment prefilter needs changed twice as often as the carbon filters, so our kit includes an extra one. RO Membranes are sold separately. Learn More
    $39.99 Special Price $33.99 As low as $27.99
  10. 4 Gallon Reverse Osmosis Tank GGN-Tank-4-Pro-3.2
    4 Gallon Reverse Osmosis Tank GGN-Tank-4-Pro-3.2
    GGN-Tank-4 - 4 Gallon RO Reverse Osmosis Tank 1/4" NPT Threads. Stainless Steel connector. This is the perfect replacement tank for most residential RO Reverse Osmosis systems. Set Air Pre Charge To 7 psi With The Tank Empty Blue color. UPC #850901003491 Learn More
    $79.99 Special Price $49.99
  11. GGN-10-2-1000
    GGN-10-2-Block Premium Quality Carbon Block Replacement Water Filter
    10 Micron Premium Carbon Block Filter. Replaces KX Carbon Block Water Filter # 10-250-190-975 Compatible Replacement. The perfect carbon block for your standard reverse osmosis system. Extruded Carbon Block Water Filter. 9 3/4" long X 2 1/2" diameter OD X 1 1/4" diameter ID. 20 per case, sold individually. Order a case and save even more. GGN-10-2-BLOCK Learn More
    $12.99 Special Price $9.99 As low as $7.79

Be sure to check our Parts Department for important parts such as TDS Testers For Reverse Osmosis Membranes, Replacement Tanks, O-rings , Filter Housing Wrenches, Faucets, Pumps, Fittings, UV Systems and more parts for your reverse osmosis pure water filtration system.   View maintenance and servicing tips online at our Installation & Trouble shooting Guide.



Simply enter your Feed Water TDS and RO Water TDS into the boxes above and click "Submit". The percentage of TDS Rejection will be displayed. We normally recommend membrane replacement once you drop below 75%. This may vary in areas with high TDS in the feed water.

See our selection of TDS meters under Water Tests