To reduce contaminants from drinking water or to improve the taste and smell of tap water, water filters in refrigerators and pitchers can do a fine job, but taking water purification to the next level often means using a reverse osmosis water filtration system.
A reverse osmosis (RO) water system integrates with the plumbing under your kitchen sink to force water through a semipermeable membrane and a series of filters, removing sediment and contaminants, providing your family with dozens of gallons of purified water each day. This guide will explore RO systems, review what factors you should consider when shopping for one, and provide a list of the top RO systems on the market.
- BEST OVERALL: Waterdrop RO Drinking Water Filtration System
- RUNNER UP: APEC Water Systems Essence Series Water Filter System
- BEST BANG FOR THE BUCK: Express Water Reverse Osmosis Filtration System
- BEST UNDER SINK: iSpring Reverse Osmosis Drinking Water Filter System
- BEST TANKLESS: Waterdrop RO Reverse Osmosis Water Filtration System
- BEST COUNTERTOP: AQUA TRU Countertop Water Filtration System
- BEST FOR APARTMENTS: RKIN AlcaPure Reverse Osmosis Countertop Water Filter
- PERFORMANCE PICK: Express Water UV Reverse Osmosis Filtration System
- BEST FOR WELL WATER: iSpring 7-Stage RO Drinking Filtration System
What to Consider When Choosing the Best Reverse Osmosis System
There are a number of factors to consider when shopping for a reverse osmosis system, including plumbing requirements, water output, the number of filtering stages, and installation demands.
Before purchasing a reverse osmosis system, it’s essential to consider a few plumbing factors. Start by checking out the space under your kitchen sink. Because it uses multiple filters and a large storage tank, a reverse osmosis system takes up a lot of real estate. That means items stored under your sink will have to go. And, if you have a garbage disposal, it may be challenging to fit a reverse osmosis system below the sink.
You’ll also need to assess the top of your sink. RO systems require a separate faucet, which typically sits adjacent to your standard kitchen faucet. This means you’ll need to install a second faucet at your sink, either by drilling through the sink edge or the countertop.
RO systems also use a dedicated air gap or non-air gap faucet. Reverse osmosis systems remove impurities by separating them from a water supply in liquid form. That liquid then must be discharged through an air gap that drips the wastewater into an outlet tube connected to the sink drain. An air gap faucet prevents the contaminated water from being drawn back into the RO system’s discharge side. If the faucet is not near the RO system and is therefore not sharing a discharge line, there is no need for an air gap faucet. Otherwise, purchase a system with an air gap faucet.
Even though an RO faucet will dispense water quickly, it refills the storage tank at the relatively slow rate of about 50 gallons per day. That translates into a water output of about 1 gallon every 30 minutes. With that in mind, you need to be selective about when to use water from the RO tap. Only use the RO faucet for drinking and cooking water. For a family with a lot of pure water needs, consider purchasing a high output system, which can produce up to 90 gallons of treated water per day, or a tankless system, which can provide up to 400 gallons of purified water.
One criticism of reverse osmosis water filtration systems is that they create a lot of wastewater. Unlike standard filters, which remove solid contaminants as the water passes through the filter, an RO system removes those contaminants in liquid form, creating wastewater called brine. A conventional RO system can produce a staggering amount of brine—between three and 25 gallons per gallon of purified water. With this in mind, look for RO systems that have a low ratio of wastewater to purified water.
RO tanks range in size from 3 gallons to 14 gallons; however, tank size can be a bit deceiving when it comes to reverse osmosis systems. The actual tank capacity will be less than what the tank is rated to hold. This is because RO storage tanks contain a metal bladder and a bubble of air to create enough pressure to push the water through the faucet when the tap is open. The actual amount of water the tank will hold varies depending on the amount of air pressure inside the tank. For example, a 4.5-gallon tank will hold around 2 to 3 gallons of water. This is important to consider as you shop for an RO tank system that will meet your family’s daily drinking water demands.
Because there is no single type of filter that can remove all contaminants by itself, reverse osmosis systems feature a series of different filters called stages. While water quality experts generally agree that four stages are enough to purify water, some systems have seven stages or more.
The filtering stages consist of a carbon filter that removes sediment; an RO membrane that removes dissolved substances from the water; a filter that removes harmful contaminants, microorganisms, and bacteria; and a post-filter that removes odor and taste from the water. Additional filters remove smaller 1-micron particles and excessive amounts of minerals like iron, lead, salt, and nitrates. Larger six- and seven-stage systems include filters that may add valuable minerals to the water lost in previous filtrations, such as calcium, and filters that improve taste and appearance.
For an RO system to work, it needs water pressure of at least 50 pounds per square inch (PSI). Most homes have water pressure between 30 and 80 pounds psi. This high pressure is needed to push the water through the various filters and still maintain adequate pressure at the tap. For homes that lack high pressure, an RO booster pump increases the water pressure at the system to up to 80 psi. Even homes that operate on standard city water pressure of 60 psi can benefit from a pump, as an RO system will run better at 80 psi or higher.
Water enters the RO system by passing through a membrane and then into the RO tank. RO systems have a shut-off valve, which is a one-way valve that prevents water in the storage tank from backflowing into the membrane when the tank is full. Once the tank is full, this spring-operated valve engages, stopping the flow of water back against the membrane, effectively holding it in the tank. The valve automatically reopens when the tank’s pressure drops enough to allow water to enter the RO system again. Though tiny and inexpensive, this valve is crucial to the proper functioning of the RO system.
Ease of Installation
The installation can be completed by the competent DIYer in as little as two hours, saving the $45 to $65 an hour it would cost a plumber to do it.
Our Top Picks
This list below represents the top standard, countertop, and tankless reverse osmosis water treatment systems from the industry’s leading manufacturers. These units feature high output and efficient wastewater to purified water ratios.
With its tankless design and high output, the Waterdrop is a premier RO filtration system. While most RO systems rely on a large tank, which eats up most of the space under your kitchen sink and limits output, this system filters water on demand. The Waterdrop provides an unending supply of treated water, as it doesn’t have to wait for the tank to refill. As a result, it can produce a whopping 400 gallons per day. This system is efficient, producing just 1 gallon of wastewater for each gallon of purified water.
The Waterdrop also includes some excellent features for monitoring the system. A multicolored LED display provides the status for each of the three filters in its seven stages and the total dissolved solid level of the filtered water in real-time. Keep in mind, however, that this new RO system technology comes with a higher price—up to twice as much as standard RO systems.
- Includes seven layers of performance filtration
- No reservoir means less space required
- 30-minute installation and 3-minute filter change
- Internal pump helps water flow faster
- Filters are not always in stock
- Water quality test discrepancies
With easy installation and high-capacity filters that last much longer than those of other systems, APEC’s RO system is an excellent option for purifying your home’s water. Whereas filters on other systems may last for only a few months, the filters on this six-stage system will last for a full year before needing replacement.
The system’s six stages remove contaminants and 99 percent of bacteria while also adding essential healthy minerals and calcium. This system produces up to 75 gallons of treated water each day. A flow restrictor and automatic shut-off valve keep wastewater production to 3 gallons for every 1 gallon of treated water. This system does use an 11-inch by 15-inch 4-gallon tank, so make sure you have plenty of space under your kitchen sink.
- Food-grade calcium added for higher alkaline rate
- Six-stage filtration system
- Includes 4-gallon reservoir
- 1:3 ratio of clean to wastewater
- MIght take a few days to clean the water
With its low price tag and 50-gallons-per-day capacity, this RO system from Express Water is an excellent option for homeowners on a budget. This five-stage system includes alkaline, ultraviolet, and deionization treatment and removes dangerous contaminants such as lead, arsenic, and chromium. A fifth stage removes taste or odor.
It’s also customizable, with the ability to add additional filtration attachments. Other features include a leak detection system. The Express Water RO system includes a simplified installation process designed specifically for DIYers. Express Water also has on-demand support from experts ready to walk you through the installation process.
- Five-stage system plus four filters included
- Color-coded parts make for easy installation
- Automatically shuts off if water leaks are detected
- Includes 4-gallon reservoir
- Challenging to maintain
- Might not produce 50 gallons per day
Capacity is often an issue when it comes to under-sink RO systems; a typical customer complaint is that their RO system just doesn’t produce enough water. That’s not the case with this system, which produces up to 75 gallons of purified water each day, which is more than enough for most families.
And while many RO filter systems stop at five stages, iSpring adds a sixth stage, which includes a remineralization filter that adds healthy minerals removed in the previous stages back into the water. In addition to its capacity and filtration system, customers also love the modern brushed nickel look for the faucet, which adds elegance and purified water to a kitchen.
- Includes 2-way water feeder for ¼- and ⅜-inch pipes
- Six-stage filtration system
- No threading pipes during installation
- Healthy minerals replaced into water
- Some reports of leaky parts
- Only works with iSpring filters
Two of the biggest complaints about RO systems are the massive tank that takes up a lot of the space under the kitchen sink and the limitations in purified water capacity. Reclaim that space and multiply your purified water output with this tankless RO system from Waterdrop. This tankless system takes up 70 percent less cabinet real estate while boosting your purified water to a whopping 400 gallons per day.
The Waterdrop also produces faster water flow, filling a cup with filtered water much faster than a standard system. The system includes compact filters that remove multiple contaminants, resulting in a unit that takes up less space. The filter design also means the filters will last much longer than the standard six months. When it is time to replace them, removing the filters is an easy twist-and-pull process.
- Tankless system allows 1:1 wastewater ratio
- Long filter life and easy to replace
- Eight layers of filtration
- Fewer hoses and pipes means less chance of leaks
- Might not work in a camper
- Some noise from the pump
The AQUA TRU countertop water filtration system allows for filtered water without taking up space under the cabinet and eliminates the need for installation.
This self-contained system is ready to go out of the box. The four-stage system removes 82 contaminants, including lead, chromium, copper, radium, and chlorine. Its quick installation twist-and-seal filters last up to two years. Fill the gallon tank and wait 12-15 minutes for the system to purify the water. And at just 18 inches wide, this system won’t take up much real estate on your counter either.
- No under-the-sink installation or potential plumbing leaks
- Long filter life
- Purifies a gallon in under 15 minutes
- Can be stored in the fridge
- Sensitive to parts being out of alignment
Just because you’re living in an apartment doesn’t mean you can’t take advantage of reverse osmosis water purification technology. This plug-and-play countertop water purifier requires no under-sink installation, making it an excellent option for those renting property. With its compact design—it’s just 9.5 inches wide—this water purifier is ideal for smaller residences. When it’s time to move out, simply pack it up and take it with you.
It features a four-stage filtration system that removes up to 99 percent of contaminants. Additional filters add beneficial minerals such as calcium and magnesium, while a post-filter removes tiny traces of impurities. The AlcaPure purifier produces a half-gallon of purified water in about 15 minutes.
- Balanced for 7 to 8 pH levels
- Rectangle block fits on counters or under cabinets
- Produces 1/2 gallon of filtered water quickly
- Three filters and a membrane to replace
- Wastewater put back into tap water basin
For high-quality drinking water under your kitchen sink, go with the system that offers the highest level of filtration. When five or even seven stages of filtration simply aren’t enough, there’s Express Water’s 11-stage RO system.
The first through fourth stages filter out sediments and remove such contaminants as arsenic, chromium, and lead. The fifth through ninth stages add valuable minerals, antioxidants, and oxygen back into your water. The final two stages include an ultraviolet sterilizer and a filter that removes odor and taste. What’s left at the other end of this system is ultra-pure drinking water. Keep in mind that the high amount of filtration this system offers does get costly when it comes time to replace the filters.
- 11-stage filtration system
- Uses UV sterilization as part of filtration
- Reintroduced healthy minerals
- Includes 4-gallon reservoir
- 1:3-4 ratio of clean to wastewater
- Hard to install under single-basin sinks
Because well water comes directly from the ground, it can sometimes require a significant amount of processing to filter out impurities and make the water palatable for drinking. With its seven-stage system, iSpring offers maximum filtration. In addition to removing harmful pollutants, this system also includes an alkaline remineralization filter that restores healthy minerals while providing an alkaline balance that improves taste.
This system also includes a crucial ultraviolet stage, which effectively removes harmful bacteria and is a must-have for those on well water. Customers love the taste of the water produced by this filtration system. The iSpring features a 75-gallon per day capacity, producing plenty of drinking water for a family.
- Filtration includes UV treatment
- Threadless connections for easier installation
- 3.2-gallon reservoir with larger tanks available
- Instructions are not easy to understand
- Some units include specific plastic parts instead of metal
We chose the Waterdrop Filtration System as our top reverse osmosis system for several reasons: no reservoir taking up space, easy to install, easily replaced filters, and a complete 7-stage filtration of over 1,000 contaminants. We also recommend the AquaTru Countertop System if you prefer a smaller filtration system.
How We Chose the Best Reverse Osmosis Systems
Since all reverse osmosis systems are designed to remove harmful chemicals and pollutants, each product on our list fulfills that requirement. Beyond that, we researched products that had different stages of filtration to meet individual needs. Some include only the basic levels of contaminant filtration, others reintroduce healthy minerals, and still others add an extra layer of filtration using UV light treatment.
Our favorite recommendations span a number of price points to help buyers looking for a reverse osmosis system that meets almost any budget. We also made sure to include systems that have little wastewater production and systems that are compatible with wells. There are also differing levels of installation difficulty, which is why we also included a couple of countertop filtration systems for buyers who just need a small amount of filtered water without a hassle.
The Advantages of Owning the Best Reverse Osmosis System
- Reverse osmosis water treatment systems offer a bevy of health benefits that make them a worthy investment for your home. The filtration process removes bacteria and microorganisms and impurities, such as arsenic, chromium, and other chemical contaminants.
- They improve the taste of drinking water. The contaminants in water can cause bitter tastes and foul smells. When RO systems remove these contaminants, the water smells and tastes cleaner.
- They eliminate the need for bottled water purchases. Although it may not seem this way when you make the initial investment in an RO system, it can save you money. Purchasing bottled water from a grocery store is considerably more expensive than filtering your own water.
- They help the environment by reducing plastic bottle waste. And while there is some debate about the impact of RO systems on the environment due to the amount of wastewater produced, they do the environment a favor by reducing the creation of plastic waste that comes from bottled water.
How to Install a Reverse Osmosis System by Yourself
Save yourself a steep plumber’s bill and read on to learn how to install a reverse osmosis water filtration system yourself.
- Shut off the cold water shut-off valve. Turn the shut-off valve clockwise to shut off the water.
- Open the faucet. This will empty the water left in the lines, minimizing leakage when you disconnect the sink’s supply valve.
- Disconnect the water line from the shut-off valve. Use a pair of pliers to unscrew and detach the supply line. Have a towel or cup handy to catch residual water in the lines.
- Connect the cold water line to the RO system. Using the adapter provided by the RO system, connect the cold water supply line to your system.
- Turn on the cold water supply valve.
- Install the filter and tank. Position the filter and tank under the sink.
- Install the drain line. Locate the system’s drain line. Drill a hole in the sink’s existing waste line, and install the waste line so your system can drain its wastewater here.
- Install the new faucet. If your sink has a predrilled hole, use this to install the new faucet. Otherwise, you’ll need to drill a new hole in the sink or countertop to mount the new faucet.
- Install the new faucet. Once the faucet is installed, the supply line attaches to the output of the RO system.
- Connect the reservoir tank to the filter system. Follow the manufacturer’s instructions to make a proper connection.
If you still have lingering concerns about your new RO system, look below for answers to the most common questions.
Q. How does a reverse osmosis system work?
Osmosis is the process of passing water molecules through a semipermeable membrane from a less-concentrated solution into a more concentrated solution. RO water filtration systems work by passing water through a semipermeable membrane under pressure. The membrane allows water molecules to pass through but does not allow larger molecules such as bacteria, viruses, urea sodium, and chlorine to pass through.
Q. What do reverse osmosis systems remove?
Reverse osmosis systems remove harmful bacteria, viruses, sediment, dirt, and a long list of toxic chemicals and compounds, including arsenic, copper, radium, cadmium, and lead.
Q. Which is better for you, distilled or reverse osmosis water?
Because the distillation system cannot altogether remove every trace of chlorine and certain pesticides and herbicides from water, RO filtration systems are more effective at purifying water.
Q. What is the difference between a single pass and a double pass RO system?
The difference between a single pass and double pass RO system is that the water produced from the first pass feeds back through the system again as the feed water for the second pass. This means the water goes through the system twice, creating a higher quality of purified water.
Q. Does the RO system have an impact on the environment?
Because RO systems do waste a considerable amount of water, they impact the environment. The average RO filtration system produces about 4 gallons of wastewater per gallon of purified water. That said, RO systems reduce the consumption of bottled water, which is considerably more damaging to the environment due to the use of non-biodegradable plastic bottles.
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