A reverse osmosis system is a specialized form of water filtration that reduces your reliance on plastic bottles by providing clean, potable water right from your tap. Most options fit underneath your kitchen sink, but countertop versions exist as well.
When comparing reverse osmosis systems, certification is an important criterion to consider. Rick Andrew, director of the National Sanitation Foundation’s Global Water Program, advises that you select a reverse osmosis system that is tested and certified to treat the specific contaminants that are impacting the drinking water supply. “Testing and certification ensure that the product is safe and structurally sound and that it will treat the water according to the claims made by the manufacturer,” he says.
We researched reverse osmosis systems from the top brands, taking into account the size of the system, speed, wastewater production, and ease of installation, as well as the taste of the water they produce. We also looked for systems that have been certified by the National Sanitation Foundation (NSF) or the Water Quality Association (WQA).
Our top pick, the APEC ROES-50 Reverse Osmosis System, is an easy-to-install under-sink system with a 4-gallon storage tank. It offers five stages of filtration.
APEC ROES-50 Reverse Osmosis System
4-gallon storage tank
5 filtration stages
Not for large households
Takes up significant space
What buyers say: 94 percent of 10,400 Amazon reviewers rate this product four stars or higher.
An under-sink reverse osmosis system such as the APEC ROES-50 offers you out-of-sight filtration with on-demand filtered water from a countertop faucet dispenser. This popular pick stands out for its straightforward operation, sizable storage tank, and five-stage filtration. According to the manufacturer, it removes 93 percent of fluoride, 95 percent of iron, and 96 percent of lead and copper. You can expect each filter to last six to 12 months, with the reverse membrane filter and carbon filters lasting up to four years before needing replacement.
The 4-gallon storage tank holds filtered water to be dispensed via the included countertop faucet. This system is rated for 50 gallons per day, which may not be sufficient for large families, but it should be plenty for households of three to four people.
The wastewater-to-clean-water ratio is unremarkable at 3:1, but it’s on par with similarly priced under-sink reverse osmosis systems. You need to devote a significant amount of under-sink cabinet space for this unit. But in return, you enjoy fresh filtered water, long filter life, and simple operation.
Price at time of publish: $180
Tank Size: 4 gallons | Output: 50 gallons per day | Filtration Stages: 5 | Filtration Method: Multi-method | Warranty: 1 year
Waterdrop Reverse Osmosis Drinking Water Filtration System
High-capacity water output
Faucet display with TDS, filter life readings
Requires minimal space under sink
Requires power supply
The Waterdrop G3 Reverse Osmosis System is one of the most popular options for homeowners who are interested in saving space and conserving water. This tankless reverse osmosis system stands out for offering a 1:1 wastewater-to-clean-water ratio. It offers fast water production and a faucet with display information regarding total dissolved solids (TDS) and filter life status. Without a water storage tank, this reverse osmosis system takes up less space under the sink. It eliminates worries over bacteria growth inside the tank. The unit measures about 18 inches tall and deep with a width just under 6 inches.
You get eight levels of water filtration when you choose this tankless reverse osmosis system. It reduces TDS, chromium, per- and polyfluorinated substances (PFAS), fluoride, arsenic salt, iron, radium nitrate, calcium, particles, chloride, chlorine, and heavy metals such as lead. All of this filtration doesn’t slow the system down; it’s rated for 400 gallons per day and can fill a glass in about 12 seconds. Three composite filters are responsible for this system’s filtration activities and feature single-turn replacement.
While some reverse osmosis systems require no power supply, that’s not the case for this tankless model. You need to plug the unit into a standard 110V outlet underneath the sink.
Price at time of publish: $646
Tank Size: Not applicable | Output: 400 gallons per day | Filtration Stages: 8 | Filtration Method: Carbon block, pleated polyester | Warranty: 1 year
Brondell RC100 H2O+ Circle Reverse Osmosis Water Filtration System
Long life for reverse osmosis membrane
Low wastewater production rate
Filter life LED on faucet dispenser
Faucet only comes in chrome
Storage tank only has 6L capacity
The Brondell H2O+ Circle is our top recommendation for a reverse osmosis water system. This under-sink model offers a compact footprint, minimizes wastewater, and features an LED filter life indicator on the faucet dispenser. Aside from these user-friendly features, this model is certified by the NSF and receives a gold seal from the WQA.
Price at time of publish: $372
Tank Size: 6 liters | Output: NA | Filtration Stages: 4 | Filtration Method: Carbon block, hollow fiber membrane, sediment | Warranty: 1 year
iSpring RCC7AK 6-Stage Under Sink Reverse Osmosis Water Filter System
Produces water with a pH greater than 7.5
Pre-pressurized storage tank
Offers six water-filtration stages
High wastewater-to-clean ratio
Confusing installation instructions
May need additional components
The iSpring RCC7AK 6-Stage Reverse Osmosis System solves one of the most common complaints surrounding filtered water, namely that it lacks "taste." This is because most reverse osmosis systems remove the minerals that give water a perceptible flavor. Our pick from iSpring includes a final remineralization treatment before dispensing filtered water, restoring the taste profile of the water filling your glass or bottle. “Remineralization is typically to enhance the flavor of the water, because reverse osmosis reduces the level of minerals in the water significantly, and some consumers prefer the taste of the water when there is enhanced mineral content,” explains Rick Andrews, of the National Sanitation Foundation’s Global Water Program. In addition to creating a natural taste, this also raises the pH of the water above 7.5, in comparison to the slightly alkaline water produced by standard reverse osmosis systems.
The first five filtration stages are intended to remove large particles such as dust, dirt, and rust, plus contaminants that include lead, fluoride, and chlorine. The final filter uses mineral stones to restore healthy levels of calcium, potassium, and magnesium to the water. The storage tank is also pre-pressurized, which produces a more consistent flow when dispensing water and is also beneficial if you connect the water line to your refrigerator.
Take note that waste water production is 3:1 with this system, making it unremarkable in terms of efficiency or water conservation. Installation can also be more challenging when compared with some other under-sink reverse osmosis systems, but it can be accomplished with basic tools and some understanding of home plumbing. A water line kit is included if you want to connect your refrigerator’s water line to the reverse osmosis system.
Price at time of publish: $279
Tank Size: 3.2 gallons | Output: 75 gallons per day | Filtration Stages: 6 | Filtration Method: Reverse osmosis, alkaline, activated carbon, carbon block | Warranty: 1 year
Brio TROE600COL Aquus Reverse Osmosis Water Tankless Filtration System
Dispenses filtered or purified water
Space-saving under-sink design
Minimal water waste
Must be plugged into an outlet
The Brio Aquus is a spendy option for a reverse osmosis system, but it frees up cabinet space under the sink while producing up to 600 gallons per day of filtered water. This tankless reverse osmosis system has four filtration stages and impresses with its efficiency. While most reverse osmosis systems produce more wastewater than clean water, this system produces only 1 gallon of wastewater for every 1.5 gallons of clean water.
Another reason to splurge on this reverse osmosis system is the dual-purpose faucet. One handle dispenses filtered water, free of sediment and chlorine, which is commonly used for cleaning or cooking. The handle on the other side of the faucet gives you a stream of purified drinking water. The LCD display on the front of the faucet provides you with a TDS reading and filter life status.
As with some other tankless reverse osmosis systems, you need to plug this unit into a standard electrical outlet. The single-unit design means that it doesn't take up much space in your sink cabinet—you just need 16.6 inches of height clearance, 18.2 inches of depth, and 5.2 inches of width to make this unit work in your space.
Price at time of publish: $550
Tank Size: Not applicable | Output: 600 gallons per day | Filtration Stages: 4 | Filtration Method: Sediment, carbon, carbon block | Warranty: 1 year
Best for Apartments
Brio ROP100 Amphora Reverse Osmosis Under Sink Filtration System
Doesn’t require drilling for installation
Single filter cartridge means easy, one-step filter changes
Pitcher base must be plugged in
Plastic components (pitcher, base) have a cheap feel
Typical reverse osmosis systems take up considerable space in the sink cabinet and require a countertop-mounted faucet dispenser. For renters, giving up a ton of space underneath the sink or installing a new fixture on the countertop may not be feasible. The good news is that reverse osmosis systems exist that require minimal installation. Our top recommendation for apartments is the Brio Amphora Reverse Osmosis Under Sink Filtration System. It offers three-stage water filtration, housed inside of a slim, tower-style unit. Filtered water is pumped to a refillable 2.5 liter carafe that sits on your countertop rather than being dispensed through a separate faucet that requires installation.
In apartments, condos, or other small spaces, this type of reverse osmosis system is a great option. The under- sink system measures 14 inches tall, with a 6.75-inch footprint. It saves considerable space by condensing the filters into a single cartridge and forgoing a storage tank for filtered water. Instead, water is pumped to a countertop carafe that sits on display with an included base. A sensor automatically refills the carafe, ensuring that you never run dry. Note that the base of the carafe must be plugged in for operation. You’ll also need a path for the tube to bring water from the filtration system to the carafe.
Price at time of publish: $250
Tank Size: 2.5 liters | Output: Not listed | Filtration Stages: 3 | Filtration Method: Carbon block, sediment | Warranty: 1 year
APEC Water Systems 90 GPD Countertop Reverse Osmosis Drinking Water System With Case
Fast, easy installation
Includes filter cartridge case
Slow flow rate
If your under-sink space is limited, or if you need greater accessibility to your water filtration system, then a countertop reverse osmosis system is an excellent alternative. The APEC Countertop Reverse Osmosis Drinking Water System sits on the counter rather than stored away under the sink. The entire system is housed in a sleek, aluminum case that conceals the filter cartridges inside.
We recommend this model for its simple installation, tool-free filter changes, and four-stage filtration that targets contaminants such as lead, chlorine, bacteria, copper, fluoride, and iron. While most people install it for long-term use, this unit is designed in such a way that it can be easily transported and set up in a new location, making it a good pick for use in rentals, RVs, or other short-term situations.
This countertop reverse osmosis system is designed to connect to most standard faucets, using a diverter valve. (It’s not compatible with specialty faucets such as pull-out or sprayer faucets.) Once connected, the system uses four filters, which, according to the manufacturer, remove 95 percent of lead, 96 percent of iron, and 100 percent of the chlorine present in tap water. It can filter up to 90 gallons per day, but you may find the flow rate to be slow if you’re filling a large container or water bottle.
Price at time of publish: $355
Tank Size: Not applicable | Output: 90 gallons per day | Filtration Stages: 4 | Filtration Method: Alkaline or calcite, coconut shell carbon, sediment | Warranty: 1 year
Whirlpool WHAROS5 Reverse Osmosis Water Filtration System
5-gallon storage tank
Easily removable/replaceable filters
Removes lead and chlorine
Undisclosed wastewater rates
Lacks space-saving design
Investing in a reverse osmosis system doesn’t have to cost a bundle. If you choose a simple system such as the Whirlpool WHAROS5 Reverse Osmosis Water Filtration System, you can have access to freshly filtered water without investing hundreds of dollars or buying cases of water on repeat. We recommend this as the best option for a budget reverse osmosis system, since it removes up to 99 percent of lead and 95 percent of chlorine, carries NSF certification, and offers easy-to-remove filter cartridges. This basic reverse osmosis system has few other features, but it produces filtered, clean-tasting water with minimal installation requirements.
This is a three-stage reverse osmosis system that primarily targets lead and chlorine. Filtered water is available to you from a large, 5-gallon storage tank that pipes water up to the included faucet dispenser. The dispenser is basic by appearance but includes an indicator light to show you when it’s time to replace the filters.
The biggest recurring expense of any reverse osmosis system is filter replacement. With this system from Whirlpool, you can expect six months of viability from the two-part pre- and post-filter set, and one to three years of use from the reverse osmosis membrane filter. When it is time to change the filters, the encapsulated design makes the filter canisters easy to detach and remove without the need for tools.
The system takes up more space than some other options, due to its larger storage tank. In addition, no data is available from the manufacturer on wastewater production. If you’re interested in an efficient reverse osmosis system that minimizes water waste, other options may be a better fit. But to kick your bottled water habit and get filtered water on-demand from your sink, the Whirlpool WHAROS5 is a solid system that is straightforward to install and maintain.
Price at time of publish: $159
Tank Size: 5 gallons | Output: 18.46 gallons per day | Filtration Stages: 3 | Filtration Method: Activated carbon, hollow fiber membrane | Warranty: Lifetime warranty available
Our top choice is the APEC ROES-50 Reverse Osmosis System since it offers five stages of filtration in a 4-gallon tank and five filtration stages. For a less pricey option, consider the Whirlpool WHAROS5 Reverse Osmosis Water Filtration System. This three-stage RO system removes the most common contaminants from drinking water and also has a 5-gallon storage tank, although it takes up more space under the sink.
What to Look For in a Reverse Osmosis Water Filter
What Water Is to Be Filtered
Reverse osmosis systems are designed to filter out contaminants that are of greatest concern in tap water, such as heavy metals like lead or chlorine, which affect the taste of drinking water. That's why you most often see RO systems mounted underneath kitchen sinks rather than in other locations where water is utilized, such as a bathroom sink or shower.
Most reverse osmosis systems have minimal plumbing requirements. You need to connect under-sink systems to the cold-water line; most kits include saddle valves for this purpose. You also need to connect the RO system to the drain line, to expel wastewater. Finally, a countertop-mounted faucet needs to be installed to dispense the filtered water, unless you choose a countertop RO system or one that directly fills a pitcher or water dispenser.
Unlike traditional water filters, not all the water pumped through a reverse osmosis filter comes out as drinkable water. Only 50 percent or less is filtered, and the rest is considered waste. When possible, avoid units with 75 percent or more waste, especially if you are treating a high volume of water per day. This unit is typically measured in ratio form, so a tank that produces 75 percent waste has a filtered-water-to-wastewater ratio of 1:3.
If you have a large household, pay attention to tank size. Filtered water is stored inside of the tank and dispensed on-demand when you fill a glass or water bottle. As the water is depleted from the tank, the system filters water to refill it. However, demand can outpace that process, which is typically slow. For this reason, most families can appreciate a water storage tank of 3 to 5 gallons. At the same time, the larger the water tank, the more space the reverse osmosis system occupies in your cabinet under the sink.
Water Output Capacity
Water output capacity of reverse osmosis systems is measured in gallons per day (GPD). Some systems for light-duty use may be rated 50 GPD, but if you use your water filtration system frequently, look for a system rated 400 to 800 GPD. Usually, higher water capacity output translates into faster fill times, too. For example, some high-output reverse systems can fill a water glass in 12 seconds or less.
How does a reverse osmosis system work?
The main difference between reverse osmosis and a more traditional filter, says Rick Andrew, director of the NSF Global Water Program, is the method in which the contaminants are removed. "A reverse osmosis system uses a semipermeable membrane to separate out the suspended and certain dissolved solids from the water," Andrew says. "On the other hand, a filter works by providing a physical barrier that the contaminants can’t pass through to separate them from the water, or an active medium that adsorbs or absorbs contaminants from the water.”
Every reverse osmosis system consists of an RO membrane, a sediment filter, a carbon filter, and several stages of filtration. When water first enters the system, it goes through pre-filtration, which usually removes sediment and or chlorine, which could clog up the membrane. Water then goes through the membrane, which further removes dissolved particles. Once the filtering is complete, the water goes to the system's storage tank, where it is ready for use. When you turn on your faucet, the filtered water comes from the storage tank through another filter in the system that polishes it for drinking.
How long does a reverse osmosis system last?
If you follow the manufacturer’s guidance for regular maintenance, including replacing filters and membranes and sanitizing the system, most reverse osmosis systems can last for 10 to 15 years or more.
How much does it cost to upkeep a reverse osmosis system?
The annual maintenance cost of a reverse osmosis system is about $50 to $100 per year if you do the regular maintenance yourself.
Why Trust The Spruce?
This article was written by Erica Puisis, a freelance home writer who has been contributing to The Spruce since 2017. When researching picks for this list, she compared various types of RO systems, including options with and without a storage tank. She evaluated the most popular models based on the wastewater of each system, filtration speed, filter maintenance, and storage tank considerations. All of our recommendations include at least three stages of filtration and have been certified by the NSF or WQA.
As part of the research process, Erica also interviewed Rick Andrew, director of the NSF Global Water Program. Rick provided insight into how reverse osmosis systems function and elaborated on the importance of choosing certified systems.