Reverse Osmosis Water Filters Buying Guide


Reverse Osmosis is a water purification technology that utilizes a semi-permeable membrane to remove 99% of contaminants from drinking water. Unlike some traditional water filters, reverse osmosis water filters are able to remove dissolved solids, and they are the only water filter system certified to remove arsenic. Much like a standard under-sink filter, the critical difference is the semi-permeable membrane that traps specific types of contaminants that carbon filters cannot.


A specialty filtration system, reverse osmosis systems are one of the most rigorous types on the market. They are especially useful for people who:

  • have chemical sensitivities
  • live with poor municipal water
  • want water as pure as possible
  • have compromised immune systems and could be at risk for infection related to waterborne contaminants
  • are concerned about certain hard-to-remove chemicals like fluoride


  • Extremely effective, cleaning out 99% of contaminants
  • Clean, crisp taste, smell and appearance
  • Flushes away contaminants instead of collecting them
  • Easy to clean
  • Powered by water pressure so no energy is needed for it to operate (dependent on system)
  • Low cost of use, pennies per gallon of filtered water


Reverse osmosis systems differ from system to system, though they typically include a pre filter (to remove large particles) and a reverse osmosis membrane, a semi-permeable membrane, which filters out a significant variety of smaller contaminants.

Our top recommended system, the USWF Tankless RO is a two filter system that sports a wide range of benefits compared to traditional tank systems. This system includes a sediment and carbon composite pre filter and an RO membrane cartridge. A high flow rate and 2:1 pure to drain waste water ratio make this system efficient and also easy to use and maintain.

In the image below you can see the breakdown of the 5 stages involved in the 5-Stage Reverse Osmosis System By Tier1. Replacement filters for this system can be found Here. These stages work together to deliver refreshing great-tasting water.

If you are interested in additional RO options like added remineralization filters for our 6-Stage Reverse Osmosis System visit our WF1010 Reverse Osmosis Alkaline Water Filter listing.


Reverse osmosis systems are uniquely capable of reducing the presence of chemicals from your home's water. In addition, the systems can reduce protozoa, bacteria, and viruses including the following contaminants:

Protozoa: Cryptosporidium, giardia

Bacteria: Campylobacter, salmonella, shigella, e. Coli

Viruses: Enteric, Hepatitis A, norovirus, rotavirus

Common chemical contaminants: arsenic, calcium chloride, chromium, copper fluoride, lead, magnesium, nitrate, phosphorous, potassium, radium, sodium and sulfate


Revere osmosis is a staged system, meaning water passes through more than one filter or stage before it's considered "clean." Here's how it works:

Stage 1: Inorganic materials are removed when water pressure pushes water through a particulate filter that's usually about 5 microns in size - it catches contaminants like dirt, rust and sediment particles.

Stage 2: Water flows through a carbon filter, where the carbon reacts to dissolved chemicals like chlorine. This step is important because chlorine and other chemicals can break down the semi permeable membrane used later in the process. Some systems will repeat this carbon filter step for greater filtration.

Stage 3: As water pressure pushes water through a semi permeable membrane, inorganic materials or contaminants are trapped. The material that is trapped is then flushed from the system and down the drain.

Stage 4: The now-filtered water is stored in a ceramic tank (because water is corrosive and can break down metals). When the tank becomes full, an auto shut off prevents additional water from flowing. The standard storage tank holds 2.5 gallons of water.

Stage 5: When the faucet is turned on, water is pulled out of the tank and through a final polishing filter that improves its taste as it pours out.


Q: What's a semi-permeable membrane?

A: Think of cellophane; the membrane is about that thick but has very tiny holes. Some can be dissolved or slowly eaten away by chemicals like chlorine.

Q: Do reverse osmosis systems use electricity?

A: Sometimes, there are some systems that incorporate electrical components. Most systems however are powered by water pressure so there's no electricity or power needed. Confirm you have an outlet available in the desired location before selecting a powered system.

Q: Will a reverse osmosis system change the taste of my water?

A: The only change you may notice is that it's cleaner, more clear and is free of the chemical taste sometimes present in water. It even makes crystal-clear ice cubes. Coffee, tea and even homemade soups can have a more robust flavor when made with water purified with a reverse osmosis system.

Q: Why do they call it reverse osmosis?

A: Reverse Osmosis is a scientific process. In regular Osmosis, water moves from an area of high water potential through a membrane to an area of low water potential (like when you get wrinkly in a pool or hot tub). Osmosis is a natural process, but Reverse Osmosis is the opposite. Water is forced through the membrane from Low potential to high (it is forced up-stream so to speak) and the water gains pressure. The membranes used in this process then remove many chemicals, ions and even molecules from the water when it is forced through them.

Q: Can I install a reverse osmosis system on my own?

A: Most reverse osmosis systems are installed by plumbers, but the process is simple and can be done by a homeowner. The system has a sequence. First sediment filter/s, carbon filter/s, the membrane, and a finishing filter (usually an inline filter). If you follow the sequence and connect the tubing in order, it should be as easy as putting together a grown-up Lego set.

Q: How often do the filters need to be replaced?

A: In general, it's recommended that you replace your filters every six months. Manufacturer will provide a recommendation specific to the design of the system, but it's commonly 6 months.


While there are a variety of reverse osmosis filtration systems available, these are highly rated:


Regular replacement of the filter and/or cartridge is critical to maintaining their effectiveness and reducing bacterial contamination. An overused or out-of-date filter can become dangerous because the filter will no longer trap contaminants, allowing them to leach back into your water. For the safety of you and your loved ones, it's important not to put off replacement too long.

There are four effective ways of knowing when it's time to replace your water filter:

  1. Follow the manufacturer's recommendations. Their specified replacement timing will err on the side of caution so you can be assured that your water quality will always be safe.
  2. Measure usage. Install a filter measurement meter or filter monitor that connects to the incoming water line that feeds the filter system and measures the number of gallons that pass through. Then using the manufacturer's recommended usage limit, program the monitor to alert you when you've reached the allowed number of gallons. You'll know exactly when it's time to replace the filter.
  3. Read your water bill. If your home is supplied with municipal water, your water bill will tell you exactly how much water is used monthly. Compare your actual usage to the manufacturer's recommendation and plan the replacement accordingly.
  4. Monitor manually. If you have non-municipal water, the most cost effective method is to monitor your filter manually-either with your palate or a water testing kit. Start with routine water tests that look for lead, microorganisms and other contaminants to verify whether your filters are still removing them. For drinking water systems, simply fill a glass with water and check the flavor yourself. You'll be able to see or taste when the filter is exhausted and no longer purifying your water because the water flavor will be unpleasant.


For answers to filter-related questions, recommendations on the best reverse osmosis system, or general drinking water questions, contact us.