Because most under-sink reverse osmosis systems look very similar and generally work the same way, it can be difficult to compare among different options.
The basics are the same in all RO systems. The water passes through a series of filters and an RO membrane to remove almost all impurities.
But the quality of filters and membrane makes a big difference in how well the system works, how long the filters last, and how the water tastes.
So when comparing among different RO systems, check the filter life, the number of stages, and the presence of a mineral filter.
Here are the most important features to compare when shopping for the best reverse osmosis system for your home.
For more help picking the right RO system, read our in-depth reverse osmosis system buying guide.
Number of Stages
Stages in a reverse osmosis system represent filters. A 5-stage RO system has five filters, including the RO membrane.
The number of stages is a good indicator of filtration performance, but only to a certain extent.
Beyond 5-7 stages, having more stages doesn’t mean the system is better at filtration. Usually, additional stages are unnecessary.
The most basic RO system should have at least five stages. These include:
Three pre-filters: Typically, one sediment filter and two carbon filters. These remove dust, sediment, organic chemicals, and chlorine. They also protect the RO membrane from damage and clogging.
RO membrane: The membrane is at the heart of the system. It deals with the hardest-to-remove contaminants such as heavy metals, dissolved salts, and microbes.
Post-filter: The post-filter polishes the water before it comes out of the faucet to remove any remaining odors and tastes.
The water that comes out of the faucet in a 5-stage system is non-mineralized. All minerals, including the good ones, have been stripped out by the membrane.
If you’d RO mineral water, look for a 6 or 7-stage system. The additional stages are mineral filters that add healthy minerals back into the water.
How Long the Filters Last
Filter life is one of the best indicators of filter quality.
Cheaper RO systems often purify water just as well as premium systems, but you need to replace the filters more frequently, usually after 3-6 months.
As for the membrane, you’ll need a new one in 1-2 years.
This not only makes maintenance a bit more involving, but it also makes the system more expensive over time.
In contrast, slightly more expensive systems have filters that can last up to a year. The membrane is suitable for 2-3 years and in some RO systems, can last up to 5 years.
If you don’t want to keep spending money on replacement filters every few months, it’s worth spending more initially on a high-quality RO system.
Another important feature to compare RO systems is the amount of water each produces in a day. This is the daily capacity, and it’s given in gallons per day (GPD).
Most RO systems produce about 70-100 gallons a day. That’s enough for most families, even large ones. If you use RO water for more than just drinking (e.g., cooking, cleaning, beverages), get a system with a daily capacity that’s within this range.
If you have a smaller family or live alone, a 30-50 GPD RO system is sufficient.
Permeate or Booster Pump
RO systems are great at cleaning up water, but it can be frustrating to get water from the RO faucet. In most systems, the purified water comes out in a slow stream that takes ages to fill a bottle or jug.
If you want an RO system that runs a bit faster, look for one with an integrated pump.
It can be a non-electric permeate pump or a booster pump, though the latter is the best at increasing water flow rate.
If you’ve spotted a good RO system, but it lacks an integrated pump, go ahead and get it. You can add a booster pump separately.
All reverse osmosis systems wastewater. The drain water contains contaminants that have accumulated on the RO membrane.
If the membrane is not regularly flushed, it will stop working after some time.
But some RO systems waste far more water than is necessary. This is often because of back pressure from the tank.
Because the tank is pressurized, it makes it harder for water to get in, especially as it fills up. So some of the water goes down the drain.
Most RO systems have a water wastage ratio of 3:1. That means that 3 gallons are drained for every gallon of purified water.
If that feels like too much-wasted water, spend a bit more on a high-efficiency system with a wastage ratio of 2:1 or 1:1.
Low-wastage systems often have an integrated permeate pump that helps water overcome backpressure, ensuring more of it goes into the tank.
Note that you can also add a permeate or booster pump separately to most RO systems. So don’t worry if your top pick doesn’t have a pump. You can always get it later.
Finally, consider the build quality of the RO system. Because it’s hard to judge build quality before you’ve bought the system, check the length of the warranty and customer reviews.
RO systems built with high-quality components typically have a longer warranty, sometimes up to 5 years.
Cheaper RO systems often come with a 1-year warranty. They may not last as long.
Check customer reviews to see how long different components have held up over time.
For some RO systems, you’ll find customers saying they had to buy their own better quality parts (usually the valves and connectors) to replace the which are ones provided by the manufacturer.
Other features to consider include tank size (3.2 gallons is ideal for most families), an auto shut-off valve to reduce water wastage and a water leak detector.
Once you’ve considered all the important features and know what kind of RO system you are looking for, you can then compare prices to find the best one according to your budget.