What to Know Before You Buy an RO Water Purifier

If you want to achieve incredible water quality, then a reverse osmosis water filter system might be the perfect solution. These systems are designed to remove almost any waterborne contaminants from your drinking water, making them one of the most effective options for homeowners who want consistently clean water on demand. Before you buy an RO water purifier for your home, it is important to understand the basics of how these systems work.

What is Osmosis?

Osmosis is a natural process that occurs on a microscopic level. In its simplest form, osmosis is a process that determines how water passes through a semipermeable membrane. A semipermeable membrane is a thin material that allows certain compounds(like water) to pass through it, but not larger compounds like rust, metals, and other contaminants. Think of these membranes like incredibly fine screens with holes in them that are significantly smaller than our eyes can see. Osmosis is all about achieving equilibrium on both sides of the membrane with regards to the total concentration of dissolved solids.

This process can seem to defy gravity by causing water on one side of the membrane to rise, but there are limits. If osmosis were a process that kept going unchecked, then a membrane with salt water on one side and fresh on the other would continue to undergo osmosis until no fresh water was left and the salt water was as diluted as possible.

The limiting factor in the osmotic process is known as the osmotic pressure. Osmotic pressure is the amount of pressure that needs to be applied to one side of the membrane in order to stop the movement of water through the membrane. Eventually, the water pressure caused by the weight of water on one side will equal the osmotic pressure and halt the flow of water through the membrane.

How do RO Systems Operate?

Not that you understand a little about how osmosis works, it is time to take a closer look at reverse osmosis. We already described how osmotic pressure can arrest the flow of water through a membrane, but what if you apply even move pressure? When that happens, water will begin to flow in the opposite direction. This means that instead of flowing towards the side of the membrane with more waterborne contaminants, the water flows away from the side with more dissolved solids.

This process of overcoming the natural osmotic flow is exactly what is happening inside of a reverse osmosis filter cartridge. Water flows from your source into the input side of the cartridge. This water will naturally contain a wide range of ions, dissolved solids, and other types of contaminants. By pressurizing the input side of the semi-permeable membrane, water is forced through the membrane towards the empty side. All of the contaminants that arrived on the input side of the membrane are left behind, while clean water is collected on the output side.

Once this process has been completed, you are left with a tiny amount of waste water on the input side and clean water on the output side of the membrane. The filtered water can then be consumed and the small amount of waste water goes down the drain. This process produces incredibly pure water due to the fact that semipermeable membranes are too fine for most common waterborne contaminants to pass through.

On a large scale, reverse osmosis water treatment can be used to turn seawater and other bodies of water with large amounts of dissolved solids into fresh drinking water. There are also a number of reverse osmosis water filtration systems that have been reduced in size order to provide the same incredible filtration power underneath your kitchen sink.

Home RO Water Systems

Reverse osmosis systems for home use have a few idiosyncrasies that make them different from other home filtration systems. One of the biggest differences between RO filters and traditional carbon block filtration systems is time. If you look at the Everpure H300, one of our most popular carbon media filtration systems, it has a filtration rate of 0.5 gallons of water per minute. This means that one of these systems could theoretically filter over 700 gallons of water per day if operated constantly. A sink reverse osmosis system like our ROM IV home RO filter will only filter 14 gallons of water per day.

This lower filtration rate is a result of the fact that you can not force water through an RO membrane too quickly without damaging the filter. It also means that, unlike other systems, most RO filtration systems operate constantly throughout the day instead of simply working when they are needed.

If you are wondering what this means when you go to pour yourself a glass of water, then you will be pleasantly surprised. Just because the water takes longer to filter does not mean that the flow rate is going to match. Most home RO systems include a storage tank that will hold a few gallons of freshly filtered water so you will always have access to clean water when you need it. This fact, combined with the fact that these systems will require multiple filtration steps, make RO filters a little larger than other systems. Even filters like our ROM IV RO systems can still fit comfortably underneath a kitchen sink even with a storage tank and three filter cartridges.


All RO filters will require multiple filtration steps. This process helps to protect the RO filter membrane itself. These membranes, with their microscopic holes, are extremely sensitive. Large particles like dirt or rust could easily clog or tear the membrane itself, limiting the effectiveness of the system as a whole. Chlorine can also damage these membranes by eroding them. Heavily chlorinated water can even “eat” holes in your filter membranes.

Most RO pre filter cartridges are similar to the cartridges found in our standard home water filtration systems. They use a carbon based filtration system to remove particulate matter and chemicals like chlorine from your drinking water. By removing chlorine and small bits of debris from your water, pre filter cartridges prepare your water to undergo reverse osmosis.

Once your water has already been filtered once, it can undergo RO filtration. The reason for performing these two different stages of filtration is the fact that RO filters are significantly finer. A pre filtration cartridge will remove contaminants as small as 5 microns in size. To give a sense of scale, half a micron is roughly 10 times smaller than the width of a strand of hair. This means that your prefiltration cartridge will remove the larger contaminants while allowing smaller particles and ions to pass through. Ions like calcium and magnesium, two of the ions responsible for lime and scale build up, can easily pass through a prefilter cartridge.

RO Cartridges

An RO cartridge’s filter membrane is designed to remove particles as small as 0.0001 microns in size! To follow our previous example, that is half a million times smaller than the width of a strand of hair! With pores this fine, you can rest assured that almost nothing but pure water is going to make it through your filtration membrane.

The fact that these membranes are designed to refilter water that has just undergone conventional filtration means that they are also designed to last. While we always recommend performing annual filter cartridge replacements, it is extremely unlikely that any home owners would experience issues with their RO cartridge before a year. Any reduction to the flow of an RO system is usually a result of the prefilter cartridge.

You may notice that we pointed out the fact that almost nothing but water can make it through an RO filter membrane. Sadly almost nothing is not nothing, and certain organic compounds may be able to pass through the membrane. In order to provide the absolute best filtration qualities, filters like our ROM IV have a final stage in the filtration process that will remove or significantly reduce the presence of any organic compounds that get through the RO membrane.

VOC Cartridge

The final stage of filtration is known as a VOC or volatile organic compound filter. This final step is important due to the fact that many VOCs have negative health effects. Many VOCs exist in gaseous form, though these gases can easily become trapped in water. Most VOC filters are manufactured using extremely fine carbon to maximize surface area and remove the largest amount of VOCs possible. Carbon’s high surface area helps to create plenty of room within the cartridge to absorb these organic compounds.

Our ROM IV Home RO System

For anyone who is looking to buy an RO water purifier, we currently offer only one home option, the Everpure ROM IV. We also carry a few options for businesses, but these would be overkill for homeowners. Even though our selection of home RO systems is limited, we don’t feel that it is missing anything. The ROM IV is a perfect system for anyone looking for the convenience of powerful RO filtration right in their home kitchen.

We have covered a few things about our ROM IV systems in this blog, but here is a quick overview. The ROM IV is a reverse osmosis system that is designed to be mounted underneath your kitchen sink. Each ROMIV system features a filterhead that holds the sediment prefilter, RO membrane filter, and VOC post filter. The ROM IV also comes with a 4.5 gallon storage tank that holds more than enough water for the average household and can be completely refilled every 9 hours. In order to dispense water from this tank, the ROM IV requires the installation of a dedicated water dispenser such as a small air gap faucet.

Despite the fact that these filters have a few more components than your average filtration system, they are surprisingly easy to install. Even if you are not familiar with plumbing, all you need is a little mechanical know how and some basic hand tools. It is important to note that you will need to add a hole to your countertop or sink prior to installation so you can install your filtered water dispenser. Depending on your kitchen, this process may require special tools.

Once you are ready to install your filter, all you have to do is find space under your kitchen sink to screw the filter head in place while leaving at least 2.5” to facilitate cartridge replacement. Once this is done, you will need to find space for the storage tank, preferably in line with the rest of the system. Once this is complete, you will add a feeder adapter to your water line so water will be diverted to the filter. The water line goes to the filter head and additional lines will have to be attached to the dispenser faucet, tank, and to the drain. Installing the drain will involve drilling a small hole in your sink’s drain pipe. These pipes are typically made of PVC plastic and are easy to drill. Once this is done and everything is all hooked up properly, you will be able to start enjoying the convenience of having freshly filtered water available on demand in just a few hours.

One of the best parts of using an RO water filter is how maintenance free they are once the installation is completed. Typically all you will have to do in terms of maintenance is replace the cartridges once per year. If you notice that the flow rate decreases before a year has passed, then replacing your sediment prefilter should fix the problem. This unparalleled convenience, combined with the amazing clean taste, is the reason why we recommend the ROM IV to any homeowner who is interested in RO filtration.

If you are ready to start enjoying amazingly fresh, filtered water whenever you want, then it is time to buy an RO water purifier. If you are curious about our ROM IV filtration systems, then feel free to reach out to a member of our team. Whether you are interested in RO or our conventional filtration systems, our filtration experts will have all of the facts you need to know. Here at efilters, our goal is to make sure that every one of our customers gets the most out of their filtration system.