Reverse osmosis removes contaminants from unfiltered water, or feed water, when pressure forces it through a semipermeable membrane. Water flows from the more concentrated side (more contaminants) of the RO membrane to the less concentrated side (fewer contaminants) to provide clean drinking water. The fresh water produced is called the permeate. The concentrated water left over is called the waste or brine.
A semipermeable membrane has small pores that block contaminants but allow water molecules to flow through. In osmosis, water becomes more concentrated as it passes through the membrane to obtain equilibrium on both sides. Reverse osmosis, however, blocks contaminants from entering the less concentrated side of the membrane. For example, when pressure is applied to a volume of saltwater during reverse osmosis, the salt is left behind and only clean water flows through.
How does a reverse osmosis system work?
Under the sink? Yes.
Reverse osmosis is most commonly installed at the point of use (POU), like under a kitchen or bathroom sink. A point-of-use RO system could also be mounted in a cabinet or remotely in the garage or basement.
For a refrigerator? Yes.
Connecting an under-sink reverse osmosis system to your refrigerator is simple and worthwhile. Reverse osmosis removes minerals from water, making your ice clear and beverages more refreshing.
For the whole house? Rarely.
Reverse osmosis can be used to treat water for the whole house. However, unless your water has a specific contaminant that requires reverse osmosis, using an RO system may be over-kill. An RO system solves specific problems like saltwater intrusion in a well or high levels of silica in the water.
An RO system will not provide the flow rate needed to pressurize an entire house. In the rare case where a whole house requires RO water, a large booster pump, like a Grundfos or Davey, provides adequate water pressure. In addition to a large water pump and storage tank, a UV system is needed to disinfect the water once it leaves the tank.
Homeowners have a lot to consider when purchasing an RO system for the whole house. If your water quality is dire enough to warrant whole house reverse osmosis, you likely have other water quality issues that will need to be addressed prior to the water reaching the RO membrane. High levels of water hardness will cause scale build-up on the membrane, reducing its performance and causing it to fail prematurely. Contaminants like iron can also foul the membrane and will need to be eliminated from the water before being treated by the reverse osmosis system.
If you believe your water quality may require whole house reverse osmosis to treat, check out our in-depth guide on reverse osmosis systems.
For showers? No.
If you don’t want to purchase a storage tank larger than your basement, reverse osmosis is not the best option for your shower. The solution is usually much simpler and more focused than reverse osmosis. Shower water with high levels of chloramines can cause nose and eye irritation and aggravate skin conditions. Chloramines are best removed by a whole house catalytic carbon filter.
Hard water can also lead to unsatisfying showers. Soap does not lather well in water with elevated mineral content, and hard water can leave hair feeling lifeless and dull. An ion exchange water softener will eliminate these contaminants.
For pools? No.
The only time you may need an RO system for a pool is if the water contains some contaminant that no other filtration system can remove. If you try to fill a 20,000-gallon pool with RO water, even with the most efficient system, you will send 10,000 gallons down the drain. Good news: the amount of dissolved solids in a pool doesn’t really matter, so other systems do a better job providing clean pool water.
For agriculture? Sometimes.
Reverse osmosis works well for hydroponic farming, but not all plants survive or thrive with RO water. RO is best suited for greenhouses where plants are misted or in small gardens, depending on the types of plants. Since hydroponic farming eliminates soil, and instead nurtures fruits and flowers with only nutrient-rich water, high-quality water is paramount to hydroponic success. Even small amounts of sediments, salts, and dissolved organics can upset the delicate balance of the plant life. RO water allows for total control over your plants nutrient intake.
For wells? Yes.
If you get your drinking water from a private well, then an RO system is an excellent way to ensure that the water flowing to your tap is safe. A reverse osmosis system is a perfect way to remove difficult contaminants often found in well water, like nitrates.
In apartments? No.
One point-of-entry unit usually supplies water to an apartment building or condominium, and installing an under-sink system is often not allowed. A countertop filter system is the best option in an apartment.
At businesses? Yes.
Commercial or industrial reverse osmosis systems are common because commercial units allow drain water to be sent back into the feed supply. Reverse osmosis removes paints, dyes, and other industrial contaminants well.
For an aquarium? Yes.
If you’re a saltwater fish enthusiast, then an RO system is perfect for you. Reverse osmosis allows you to strip all minerals from the water and add exactly the amount of salt you need back in with a remineralizing filter. Most aquarists rely on a combination of reverse osmosis and deionization (known as RO/DI water) to ensure their fish are immersed in highly pure water, modified to match the fish's natural environment.
| Learn more about why you should use reverse osmosis water in your aquarium. |
In RVs? Yes.
RO systems require proper draining. Storage tanks are difficult to attach to RVs because drain hookups aren’t located at campsites, but it is possible. A reverse osmosis system can be very helpful for those whose RV adventures take them into more remote, wilderness locations. A combination of RO and ultraviolet disinfection can make sure the water you are drinking is free from harmful bacteria and particulate matter.
| Explore our RV water filters buyer's guide. |
Reverse osmosis systems usually last between 10 and 15 years. While the systems themselves have a long lifespan, the RO membrane and filters need replacing periodically. The prefilters and post filters should be changed every 6 months to 1 year. Depending on your water conditions, the RO membrane should be replaced every 2-4 years.
Here are a few tips to help you maintain your reverse osmosis system.