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What is Reverse Osmosis? Facts and How it Works

by Peter Lombardi

Quality Specialist, Consultant

> 4 min read


Cleaning your tap water isn’t always a straightforward process, especially if you’re worried about multiple potential contaminants. Sediment and activated carbon filtering remove many problems, but there are limitations in how many dissolved minerals they can remove. Areas with high levels of iron, calcium, and fluoride require stronger filtration.

Reverse osmosis uses extremely fine filtration membranes to remove dissolved minerals, bacteria, chemicals, and other water contaminants. Although it cannot remove every potential threat, this filter style is reliable and will last for years with minimal maintenance. Here’s what you need to know about reverse osmosis’s strengths and limitations.

HERE ARE OTHER QUESTIONS THAT YOU MIGHT HAVE ABOUT WATER:

What Is Reverse Osmosis?

Reverse osmosis is a type of filtration that uses a spiral-shaped system of membranes. Water is pumped into the system and pushed through the filters, which are fine enough to keep most contaminants out. The wastewater is then run off through a separate pipe while the clean water continues to your faucet.

It’s one of the most expensive filtration systems available for home water systems because of its complex and effective reverse osmosis. However, it’s so effective and consistent that it’s frequently used for filtering a variety of chemicals in scientific laboratories and other facilities that require a high level of cleanliness.

Targets For Removal

Reverse osmosis can remove sodium, lead, bacteria, fluoride, ions, and other particles larger than .0005 μm. Even most dissolved chemicals are larger than this, so it’s highly effective at eliminating nearly all contaminants. Most reverse osmosis systems have separate sediment filters and chlorine filters in front of the main reverse osmosis membranes.

Reverse osmosis systems can capture some chlorine quantities, but if your water is highly chlorinated, some may still slip through. The membrane also cannot filter all pesticides because of how much they dissolve in water. If pesticides are a concern in your area, you may need a carbon block filter in addition to your reverse osmosis system.

The mineral removal process of reverse osmosis will slightly reduce your water’s pH, whether you want it to or not. You can adjust this with an alkaline ionizer if desired, but many families leave it as-is, especially if their water is slightly alkaline, to begin with.

Who Needs Reverse Osmosis?

Reverse osmosis is a stellar option for any family, especially since municipal water infrastructure is imperfect. Even if your city’s water system has a historical track record for being safe and reliable, a water main break or gradual breakdown in the pipes could affect the water’s quality.

However, reverse osmosis system installation is most urgent for well water users. Well water is usually drawn from at least 10’ underground, but runoff from nearby farms, factories, and landfills can easily penetrate this depth. Wells at least 50’ deep resist contamination better than shallow wells, but chemical runoff can still reach hundreds of feet underground eventually.

How to Use Reverse Osmosis Properly

Reverse osmosis can be expensive to maintain, and it's helpful to use a separate large sediment filter before the water reaches the reverse osmosis filter. Although the membranes in reverse osmosis systems do not clog easily, large sediment can still cause problems if enough builds up.

Because reverse osmosis has a relatively slow flow rate, most systems use a pressurized tank to keep a larger supply of filtered water on hand at all times. This makes it easier to get enough water for cooking and cleaning at one time without waiting for the system to filter each drop.

If you use too much water at one time, you may notice the pressure drop while the tank refills. This isn’t a problem if it happens occasionally, but you might want to invest in a larger tank if it occurs regularly.

In the event of a boil advisory from your local authorities, your reverse osmosis filter will be able to act in place of boiling the water for up to 24 hours. After that, you will need to replace the filter and sanitize the tank, making sure to boil your water while that process is happening. Even in a short-term boil advisory, make sure to replace the filter and sanitize thoroughly afterward.

Does Your Whole House Need Reverse Osmosis?

Keep in mind that you don’t necessarily need reverse osmosis for your whole house. Although reverse osmosis can improve your laundry quality and make your showers more comfortable, you can achieve similar effects with other filter types. Having reverse osmosis in your kitchen alone will still help protect your family’s health and well-being.

However, reverse osmosis may be the safest overall option for your home if your well water is of poor quality or has specific chemical contaminants that other filters can’t handle. If someone in your family has very sensitive skin or pre-existing conditions that make them more susceptible to water-related health problems, reverse osmosis is your safest bet. 

Installing a Reverse Osmosis System

Most reverse osmosis systems are designed to fit easily under your kitchen sink. Their exact dimensions vary, but most aren’t much larger than a few gallons. Many have clearly labeled instructions and designs that make them easy for homeowners to install independently.

Once you install the filter, you will need to change the sediment and chlorine pre-filters once every 12 months. If your system does not include these filters, you should purchase and install them separately and maintain them per their own directions.

The reverse osmosis membrane only needs replacing once every 2 or 3 years. The final filter will need occasional replacement as well, but this time frame varies between manufacturers. Overall, these systems are very low maintenance, making them a fantastic choice for busy families who want high-quality water without relying on water bottles.


Is Reverse Osmosis Right for Me?

Since reverse osmosis provides high-quality drinking and cooking water, it’s a fantastic choice for families of all sizes. These systems fit easily under your sink, so they’re great for small farmhouses, cabins, and other remote locations, as well as suburban and urban homes.

Make sure to keep track of when your filters need changing to make the most of your system. With proper installation and some occasional maintenance, you’ll notice a consistent improvement in your water quality.

Peter Lombardi

About the Author

Peter is a Los Angeles based water quality specialist, and works as a surveyor for businesses and communities looking to be informed and active about the quality of their water. He shares his expertise with 64 oz. to ensure everything is accurate, and to prevent the spread of misinformation about water contaminants.