What Is a Reverse Osmosis System and How Does It Work?

Posted by
John Woodard on October 16, 2023

Widely considered one of the most effective water filtration methods, reverse osmosis (RO) creates clean, great-tasting water. RO systems are used in a variety of applications, including filtration for whole houses, faucets, aquariums, and restaurants. No matter what kind of water you start out with, there is likely an RO system that will suit your needs. Below you will find what reverse osmosis systems are, how they are beneficial, and what they are used for. You can also find a list of the best reverse osmosis systems on the market.

What is reverse osmosis?

Reverse osmosis is a multi-stage water treatment process that removes contaminants from unfiltered water, or feed water, when pressure forces it through a semipermeable membrane. Residential reverse osmosis systems utilize at least three stages of treatment to reduce levels of virtually all contaminant types. In the final stage, the RO membrane, water flows from the more concentrated side (more contaminants) of the 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.

How does reverse osmosis work?

Reverse osmosis utilizes a semipermeable membrane with very small pores that traps contaminants while water is pushed 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.

What is a Reverse Osmosis System and How Does it Work?

How does a reverse osmosis system work?

 reverse osmosis system removes sediment and chlorine from water with a prefilter before it forces water through a semipermeable membrane to remove dissolved solids. After water exits the RO membrane, it passes through a postfilter to polish the drinking water before it enters a dedicated faucet. Reverse osmosis systems have various stages depending on their number of prefilters and postfilters. 

Stages of RO systems

The RO membrane is the focal point of a reverse osmosis system, but an RO system also includes other types of filtration. RO systems are made up of 3, 4, or 5 stages of filtration. 

Every reverse osmosis water system contains a sediment filter and a carbon filter in addition to the RO membrane. The filters are called either prefilters or postfilters depending on whether water passes through them before or after it passes through the membrane.

Each type of system contains one or more of the following filters:

  • Sediment filterReduces particles like dirt, dust, and rust
  • Carbon filterReduces volatile organic compounds (VOCs), chlorine, and other contaminants that give water a bad taste or odor
  • Semipermeable membraneRemoves up to 98% of total dissolved solids (TDS)

Learn more: Stages of reverse osmosis systems

How a Reverse Osmosis System Works

  1. When water first enters an RO system, it goes through prefiltration. Prefiltration typically includes a carbon filter and a sediment filter to remove sediment and chlorine that could clog or damage the RO membrane.
  2. Next, water goes through the reverse osmosis membrane where dissolved particles, even too small to be seen with an electron microscope, are removed.
  3. After filtration, water flows to the storage tank, where it is held until needed. A reverse osmosis system continues to filter water until the storage tank is full and then shuts off.
  4. Once you turn on your drinking water faucet, water comes out of the storage tank through another postfilter to polish drinking water before it gets to your faucet.

Why do you need an RO storage tank?

An RO storage tank holds reverse osmosis water so you have plenty to use when you need it. A reverse osmosis system outputs water slowly. It takes one minute to produce two to three ounces of RO water. If you were to turn on your faucet for a glass of water at the actual membrane production rate, then you would have to wait at least 5 minutes for it to fill. With a storage tank, your glass fills instantly.

Learn more: How a water storage tank works

What does reverse osmosis remove?

Reverse osmosis removes chlorine, salt, PFAS, and dissolved solids like arsenic and fluoride through the RO membrane. RO systems also include sediment and carbon filtration for a broad spectrum of reduction. The carbon filters in an RO system remove chlorine, bad taste, and foul odors, and the sediment filter removes dirt and debris.

Reverse osmosis removes

  • Fluoride
  • Salt
  • Sediment
  • Chlorine
  • Arsenic
  • VOCs
  • PFAS
  • Microplastics
  • Herbicides and pesticides
  • Heavy metals
  • Many other contaminants

The contaminants listed are some of the most popular ones treated with an RO system, but the system also removes a slew of other contaminants.

Reverse osmosis systems do not remove some bacteria and viruses. If your water comes from a city treatment plant, then it should already be microbiologically safe. Reverse osmosis may remove some bacteria, but bacteria could grow on the membrane and potentially enter your water supply. To remove living organisms and viruses, we recommend UV disinfection.

Learn more: How to remove bacteria from your drinking water

What pretreatment does a reverse osmosis system need?

Pretreatment can greatly extend the life of a reverse osmosis membrane when water quality is poor. When certain minerals, bacteria, chemicals, or other substances contaminate water as it flows through an RO membrane, they can absorb or form deposits on the membrane. The buildup of contaminants in an RO membrane is known as membrane fouling, and the forming of inorganic deposits is known as membrane scaling. To prevent membrane fouling and scaling, you must remove the contaminants before they can harm your RO membrane. Different contaminants require different pretreatment solutions, so you must know the makeup of your water before deciding on an appropriate pretreatment system. Well water, for example, will need more thorough prefiltration than city-treated water.

How to prevent biofouling in a reverse osmosis system

Biofouling is the result of the buildup of biological contamination on a reverse osmosis membrane. City-treated water should be free of microbiological contaminants unless a boil water advisory is issued, so homeowners with well water should be the ones most concerned with biofouling. To get rid of biofouling, you must get rid of the microorganisms that make their way to the membrane. The most practical method for biofouling prevention for reverse osmosis is ultraviolet disinfection.

Ultraviolet (UV) water disinfection systems deactivate microorganisms with UV light, preventing bacteria, viruses, parasites, and other microorganisms from reproducing. When using a UV disinfection system, ensure that you install a sediment filter before the UV system. If not paired with a sediment filter, dirt, debris, and sediment particles can hinder the effectiveness of the UV system. If your home uses well water, incorporating a UV system into your home well water system is essential in keeping you and your family safe from waterborne illness.

Learn more: What is a UV water purifier and how does it work?

How to prevent membrane scaling in a reverse osmosis system

Reverse osmosis membrane scaling can be resolved by a few pretreatment solutions. Two common residential pretreatment solutions for dealing with membrane scaling are water softeners and scale inhibitors.

Water softeners

Water softeners exchange sodium or potassium ions from a brine with calcium and magnesium ions in hard water. Because of how they operate, water softeners are commonly called ion exchange systems. Hard water can be treated by a reverse osmosis membrane, but it will greatly shorten its lifespan. As a result, water softening is the most efficient way to receive high-quality soft water from a reverse osmosis system while elongating the lifespan of the membrane. Water softeners are also a practical method for preventing scale buildup in residential RO systems.

Learn more: What is a water softener and how does it work?

Scale inhibitors

Scale inhibitors are chemicals that are added to feed water delivered to an RO system. These chemicals increase the amount of inorganic compounds that water can dissolve, allowing the system to operate at a higher production rate. Scale inhibitors are excellent for dealing with the two most common inorganic salts in water, calcium carbonate and calcium sulphate. They are also effective across a wide pH range, safe to handle and use. Feed water should contain low levels of iron, a common well water contaminant, when using a scale inhibitor to prevent iron from reducing the efficacy of the inhibitor.

Learn more: How to recognize membrane foulants

Do reverse osmosis systems need a booster pump?

Reverse osmosis booster pumps are essential if your home’s water pressure is below 40 psi. If your water pressure is between 40 and 50 psi and your water’s TDS levels are over 500 ppm, you should also use a booster pump. If you do not use an RO booster pump and you have low water pressure, your RO system will not produce water as efficiently or effectively as it is can. Homes that use city-treated water rarely need an RO booster pump, but homes with well water are more likely to experience low water pressure that necessitates a booster pump.

Learn more: What is a reverse osmosis booster pump and how does it work?

Do reverse osmosis systems need a permeate pump?

Permeate pumps allow reverse osmosis systems to run more efficiently, but not all RO systems are plumbed to use one. If your system is plumbed for a permeate pump, it will allow your system’s efficiency to increase by up to 80 percent. It saves water by using energy from reject water to pump permeate water to the storage tank. This allows your RO system to use up to 80 percent less water than a system without a permeate pump. Most reverse osmosis systems waste about four gallons of water for every one gallon of clean water produced, but a permeate pump allows an even ratio between water sent to the drain and clean water pumped to the storage tank. If a permeate pump is compatible with your RO system, installing one will save you a significant number of gallons of water each year.

Learn more: How a permeate pump works with a reverse osmosis system

Reverse osmosis system benefits

A reverse osmosis system is one of the most extensive methods of filtration. It removes 98% of dissolved solids, which makes it healthier to drink. A water distiller is the only other drinking water system that also reduces TDS, but it's less efficient than an RO system. 

  • Reduces harmful dissolved contaminants
  • Reduces sodium
  • Removes foul tastes and odors
  • More environmentally friendly than bottled water
  • Easy to install and maintain
  • Fits under the kitchen sink

Browse Reverse Osmosis Systems

3 best reverse osmosis systems

Neo-Pure Residential 4 Stage Reverse Osmosis System

Benefits

  • Many configuration options
  • Comes preassembled
  • Excellent value
  • Simple installation and maintenance
  • Permeate pump included
  • Remineralization postfilter

Multiple configurations

The Neo-Pure Residential 4 Stage Reverse Osmosis System comes with one of three membrane sizes: 25, 50, and 75 GPD. You can also choose between a 3.2-gallon and a 4.5-gallon storage tank for your system. These configurations allow you to select the best system for the needs of your home. We recommend the following configurations based on household size:

  • Family of 4 or fewer – 25 GPD
  • Family of 4 or more – 50 GPD
  • Light commercial use – 75 GPD

Easy installation and maintenance

This system delivers to your door preassembled. As a result, the installation process is simple. Alongside its easy installation, the Neo-Pure’s quarter-turn cartridge replacement system makes routine maintenance simple and quick. The replacement cartridges for this system are industry standard, keeping maintenance costs at a minimum. Only the cartridges, not the plastic housings, reach the landfill, minimizing plastic waste.

Remineralization postfilter

The Neo-Pure remineralization cartridge reintroduces beneficial calcium back into the filtered water while also raising alkalinity and pH. This filter gives the final product a pleasant, refreshing flavor that is ideal for drinking and cooking.

How often to replace cartridges

Neo-Pure systems offer the convenience of purchasing 6-month and 12-month cartridge replacement kits. These kits provide all the components you need to keep your system up and running. The 6-month kit includes two 5-micron carbon block filters and one inline remineralization filter. The 12-month kit includes two 5-micron carbon block filters, one inline mineralization filter, one RO membrane filter, and an RO sanitizing maintenance kit. When purchasing a 12-month kit, ensure you select the product with the correct RO membrane output.

Shop 12-month kits by size: 25 GPD | 50 GPD | 75 GPD

Aqua Flo 4 Stage Quick Change Reverse Osmosis System

Benefits

  • Easy to install
  • Customizable to local water conditions
  • Lead-free faucet included
  • Easy filter replacements

Quick filter changes

The Aqua Flo QCRO system boasts a twist and lock design, making filter changes quick and simple. The 4-stage system can also be customized to accommodate changing water conditions.

Easy installation

Because of its design, the Aqua Flo QCRO system is simple to install. Color-coded tubing and quick-connect fittings make connecting this system uncomplicated. The QCRO also comes with a John Guest angle stop adapter to further simplify the installation process.

How often to replace the RO filters

Pentair Freshpoint POU 3 Stage

Benefits

  • Fits in tight spaces
  • Click-to-lock filter cartridges
  • Color-coded cartridges
  • Easy installation

Compact design

The Pentair Freshpoint is an excellent system because of its compact design. The filter housings open toward you, allowing you to pull the filter forward and replace it in no time. Other under-sink RO systems need additional clearance above or below to remove the housings and change the filters. 

Click-to-lock cartridges

The FreshPoint filters are considered "quick-change" because they can be replaced with a single click. Keep in mind that ease of maintenance comes at a cost to the environment. The FreshPoint filters are encased in plastic that will end up in a landfill. 

How often to replace the RO filters

    Does reverse osmosis waste water?

    Most reverse osmosis systems waste about four gallons of water for every one gallon produced. Unlike other filters that trap contaminants, a reverse osmosis system sends water with rejected contaminants down the drain as wastewater. As water flows through the system, it is divided into two streams. One stream carries the filtered water to a dedicated faucet, and the other stream carries the removed salts, dissolved pollutants, and minerals to the drain.

    The brine or "wastewater" carries rejected contaminants from a reverse osmosis system to the drain. However, the brine water is used for a purpose, so it is not exactly wasted. The wastewater in an RO system helps clean the water, just like a dishwasher uses water to clean dishes or a washing machine uses water to clean clothes. However, it is our job to care for the environment to minimize the amount of water sent to the drain and increase the efficiency of the RO system.

    How to reduce wastewater in an RO system

    1. Add a permeate pump. Installing a permeate pump to a reverse osmosis system is the best way to increase its efficiency. Permeate pumps reduce the wastewater from an RO system by 75 to 80%. Not every reverse osmosis system is designed to use one, so make sure the one you choose is plumbed for an additional pump.  
    2. Choose an RO system with an automatic shut off valve (ASO). An ASO valve stops the flow of water to the drain once the storage tank is full.
    3. Use the RO reject water for landscaping or artificial lakes. Drain water has higher levels of total dissolved solids (TDS), but it is safe to use in your lawn or garden.

    Is reverse osmosis good for the environment?

    When the water you use drains from your home, chemicals and other contaminants must be removed before it's recycled. Wastewater is either sent to a water treatment plant and diluted to make it easier to treat or to riverbeds for nature to filter through the hydrologic cycle.

    A reverse osmosis system makes waste treatment more efficient. Reverse osmosis water drained from your home is already free of chemicals since they have been removed in the carbon filtration stage. The leftover brine water has just a slightly higher concentration of dissolved inorganics. RO systems speed up the recycling process because no new chemicals are introduced into the water supply after RO water drains from your house.

    Reverse osmosis vs. bottled water

    Most bottled water is purified through reverse osmosis, but producing bottled water wastes more water than a reverse osmosis system. Think about all the water required to make one bottle of water. When bottled water is purified, wastewater is sent to the drain, and producing the bottle uses water and petroleum. Petroleum is used again to deliver the bottled water to the store. Afterward, the truck may get washed, using even more water. A reverse osmosis system provides water that is just as pure and refreshing as bottled water while also dealing a smaller environmental impact.

    Reverse osmosis also has the added benefit of perpetually producing highly purified water in your home. There is no need to run out to the grocery store to stock up on expensive and wasteful cases of bottled water. A reverse osmosis system produces bottled water quality hydration in the comfort of your kitchen. You can even fill stainless steel water bottles with RO water and store them in your fridge, so you can enjoy all the conveniences of bottled water without the disposable single-use plastic bottles and weekly grocery runs.

    plastic water bottle waste

    Is reverse osmosis water good for you?

    A reverse osmosis water system removes dissolved contaminants that you can't see but that could make you sick. Reverse osmosis does work for your kidneys by filtering water before it enters your body. It also removes beneficial minerals like calcium and magnesium from water, but that does not make reverse osmosis water bad for you.

    Our bodies are 70-80% water that hydrates, lubricates joints, and aids organ function. You don’t need minerals to do those things. You would have to drink excessive amounts of water for your body to absorb enough mineral content to make a significant difference. Food is the primary source of essential nutrients, not water. If you want more minerals, eat your fruits and veggies.

    Some mineral content is fine to drink, but the EPA recommends that the amount of TDS in water not exceed 500 parts per million. A large portion of the U.S. has TDS levels that exceed this level and could benefit from an RO system.

    Where to use a reverse osmosis system

    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 whole-house reverse osmosis systems.

    Learn more: How water booster pumps work

    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.

    Learn more: Reverse osmosis water for hydroponics | How hydroponic systems work

    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.

    Learn more: Countertop filter buyer's guide

    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 are 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: 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. 

    Learn more: RV water filters buyer's guide

    washing dishes in RV

    Reverse osmosis system vs. a water softener

    Unlike a reverse osmosis system, a water softener does not filter harmful contaminants from water. It removes calcium and magnesium to soften hard water and make washing clothes and showering easier.

    Water is softened during reverse osmosis. However, using a reverse osmosis system to treat hard water (above 7 grains) shortens the life of the RO membrane. This will lead to more frequent membrane replacements. If you have hard water, use a water softener to treat it instead.

    Reverse osmosis systems and water softeners benefit each other. A water softener installed before the RO system removes iron from the water that can stain your shower, clothes, and toilet and clog the RO membrane. An RO system removes sodium added by the water softener.

    Learn more: How water softeners work

    How long do reverse osmosis systems last?

    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

    If your RO system isn't working properly, this RO Troubleshooting Guide will help you find and fix the problem. 

    8 things to consider when searching for a reverse osmosis system

    1. Water source

    The water that enters your home feeds the reverse osmosis system. City water or municipally treated water is relatively free of chemicals and bacteria but may contain inorganic dissolved solids, which an RO system is designed to reduce. Private well water could contain harmful pathogens and chemicals in addition to dissolved solids.

    Reverse osmosis systems can treat both city and well water, as long as the well water has been pretreated for bacteria and particles that could clog the membrane. If your home's well water is contaminated with heavy metals like arsenic, then you may need a UV system to disinfect the water once it leaves the storage tank.

    2. Water demand

    Consider how much water you and your family are going to use. Every person, according to nutritionists, should drink half their weight in ounces every day. For example, if you weigh 160 pounds, then you should be drinking 80 ounces of water per day. You also must take water used in ice machines, refrigerators, and all your other appliances into account. Each reverse osmosis system provides the amount of water produced each day, measured in GPD (gallons per day).

    3. Water pressure

    Reverse osmosis uses water pressure to force clean water through the membrane. If your household water pressure is below 40 psi, then you need to increase the pressure for reverse osmosis with an RO booster pump. If you are on well water supply, make sure your tank’s water pressure is set high enough for an RO system to work. A high level of dissolved solids in water also increases the amount of pressure needed for the RO system to produce clean water.
    A residential reverse osmosis system is point-of-use, which means you install it right where you need the RO water. Most RO systems install directly under your sink. Whole house reverse osmosis systems are used less often because they require a large storage tank and booster pump for adequate pressure to supply water to every point in your house.

    4. RO style

    Reverse osmosis systems come three different cartridge styles: quick-change, drop-in, and standard. Your choice of filter style depends on whether you prefer easy maintenance, low maintenance cost, or the least environmental impact.

    Quick-change cartridges: simplest to maintain, but also the most expensive and the least environmentally friendly

    Quick-change filters are easy to replace. Simply twist the filter and pull it out. Then, take the new filter and turn it in the opposite direction to replace the old one. However, the ease of maintenance comes with a high price tag, and the filter cartridges are made of plastic that gets wasted every time an old filter is discarded.

    Drop-in and standard cartridges: More difficult to replace, but also the least expensive and most environmentally friendly.

    To replace a drop-in or standard filter, unscrew the housing, throw the filter cartridge away, put a new cartridge in, and put the housing back in its place. Standard filters can be replaced with compatible cartridges, but drop-in systems require exact replacements.

    Reverse osmosis systems also come in different stages, usually three, four, or five, based on the number of prefilters and postfilters included. The RO membrane does most of the work removing dissolved solids, but additional prefilters and postfilters can polish, re-mineralize, and provide additional chlorine and sediment removal. Eventually, the membrane wears out, but prefilters give an initial pass-through filter media to help extend the life of the membrane.

    5. Budget

    When budgeting for a reverse osmosis system, you have several factors to consider: How much does the system cost? How much will installation cost, especially if you hire someone? How much does on-going maintenance cost? These factors may affect which RO system you choose or whether or not you use one at all.

    The price of a reverse osmosis system varies depending on whether you need one under your sink or for your whole house and how many additional components you need. Whole house RO systems are much more expensive and complex. Under-sink RO systems usually range from $200 to $400 depending on the style. The cost increases if the system includes a booster pump, permeate pump, storage tank, or pretreatment.

    Installing any RO system is an investment that requires on-going maintenance costs, including replacement filters and membranes. The replacement cost and frequency depend on your style of an RO system. Generally, the RO membrane needs replacing every two years, and the filters need replacing every six months to one year. The reverse osmosis system itself lasts twenty years or longer with proper care.

    Factors that influence the cost of an RO system:

    • Type of system
    • Pretreatment
    • Installation cost
    • Maintenance cost
    • Additional components

    6. Ease of Installation

    Most under-sink reverse osmosis systems are easy to install. However, installing an under-sink RO system requires a dedicated faucet, which means you may have to drill a hole in your countertop. If you're not comfortable doing this job yourself, then you may need assistance from a plumber or a handy friend or family member.

    Reverse osmosis systems must have a dedicated faucet and a drain connection to prevent the dirty drain water from flowing back into the clean drinking water. An RO system cross-connects the drain line and the water line. Plumbing code requires that cross-connections have an air gap faucet that allows drain water to pass through without returning to the clean water.

    Learn more: How to fix an air gap leak.

    Consult a water specialist before installing a whole house reverse osmosis system to make sure there is not a simpler, equally effective solution and to make sure you apply proper pretreatment based on your water conditions.

    7. Efficiency 

    A reverse osmosis system is not the most efficient filter. After reverse osmosis filters contaminants, it sends them to the drain with a significant amount of water. However, this water is not exactly wasted since it is used to carry contaminants away and make potable water.

    Standard water filters collect contaminants on their surface, but the RO membrane stops them and uses water to carry them to the drain. Adding a permeate pump to your RO system makes it 85% more efficient. The permeate pump uses the wastewater as energy to send clean water to the storage tank. The most environmentally friendly RO systems include a permeate pump or allow you to add one.

    Learn more: How a permeate pump works with a reverse osmosis system.

    permeate pump chart

    8. Remineralization

    Reverse osmosis removes dissolved solids from water and reduces alkalinity or lowers water's pH in the process. The lower pH makes the water slightly acidic. Acidic water is corrosive, but adding an acid-neutralizing filter, like a calcite filter or alkaline water filter, increases the pH adds mineral flavor. The Aptera filter dissolves calcium and magnesium in water and reduces scale, microorganisms, and sediment through several stages of remineralization.

    water pH scale

    Download The Reverse Osmosis FAQ Guide And Call Our Water Experts

     

    Comments 11-20 of 20
    Can minerals removed by RO System be re-injected into the water for drinking ? If yes, how ?
    DK Jadhav on June 01, 2020
    I am debating on putting an RO system in my home but have a couple of questions. Is it necessary to put the filters under the sink with the tank? Is there any reason I couldn’t put the filters in my garage, which is about 30’ away from the kitchen sink? Seems like it would make filter maintenance/upkeep a lot easier. Thanks in advance for your help.
    Bryan on July 02, 2020
    Why RO can be used for agriculture? Why not all plants survive or thrive with RO water ?
    Telma on January 15, 2021

    Hello Victoria,

    Reverse osmosis can be very helpful for people on well water! However, before installing an RO unit beneath your sink, you want to make sure you have appropriate pretreatment first.

    Often, well water presents multiple contaminants that can be hazardous to health or damaging to plumbing and appliances. If your well water is hard, you want to make sure you have a water softener before the RO unit. The minerals in hard water can damage the membrane. If your well has sediment or particulate matter, high concentrations of iron, or bacteria, you will want to make sure that it is eliminated from the water before it reaches the reverse osmosis membrane to ensure optimal performance.

    That being said, RO is very effective at reducing many contaminants found in well water. If the water is properly pretreated, it can be an excellent way to keep your water safe.

    John Woodard, Master Water Specialist on March 12, 2020
    Is RO good for people who have well water?
    Victoria Trybul on March 12, 2020

    Great question, Peter!

    While the RO membrane is capable of removing bacteria and viruses from water, it is not recommended to use an RO system for this purpose. Bacteria can cause the RO membrane to deteriorate, and create pinhole leaks that could allow bacteria to be reintroduced to your water supply. Furthermore, the O-ring seals on RO units are not designed to prevent bacteria from migrating. As you quoted from the article, it is also possible for bacteria to proliferate on the membrane. Here’s a link to scientific journal that examined bacterial growth and membrane fouling in RO: https://link.springer.com/article/10.1007/s13201-016-0493-1

    Most spec sheets for residential RO systems will specify that the system should only be used on potable water and not microbiologically unsafe water. (Some examples: https://assets.freshwatersystems.com/images/j5emwk2v0hsgxlks3anh/NeoPure-RO4300RX-SpecSheet.pdf and https://assets.freshwatersystems.com/images/znrfrmfmpzjafimdltw5/PurolineManual.pdf and https://assets.freshwatersystems.com/images/psal1biiycmdl6hrohph/3MRO401_Data_Sheet.pdf).

    So, while it is technically possible for RO membranes to remove bacteria, if your water is microbiologically unsafe, UV disinfection is a much stronger choice. UV light neutralizes the DNA of the bacteria and viruses, rendering them incapable of reproduction. This is a much safer alternative than the mechanical rejection of the RO membrane.

    Hopefully this helped clarify your question!

    John Woodard, Master Water Specialist on January 08, 2020
    “Bacteria and Viruses? No. If your water comes from a city treatment plant, then it should already be microbiologically safe. Reverse osmosis may remove some bacteria, but bacteria could grow on the membrane and potentially enter your water supply. To remove living organisms and viruses, we recommend UV disinfection” do you have some documentation saying RO membrane does not remove bacteria and viruses
    peter rodrigues on January 08, 2020
    We installed hoses and couplings in our motorhome so that we can move our RO system from home to rv.

    My wife has a digestive sensitivity to chlorine and many minerals, so this goes a long way to keeping her healthy and comfortable.

    Clyde Janssen on December 18, 2019

    Hello Ellouise!

    Most CPAP manufacturers recommend using distilled water for CPAP machines. This is because using distilled water is sterile, and prevents any mineral build-up or bacterial growth from setting in the humidification chamber. However, a well maintained reverse osmosis system will remove 98% of dissolved solids from your water, making RO water a safe alternative for use in a CPAP machine. However, most CPAP manufacturers do not recommend long term use of RO water in CPAP machines.

    John Woodard, Master Water Specialist on October 21, 2019
    Is this water safe for my CPAP
    Ellouise Wilson on October 21, 2019
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