In a reverse osmosis system, the process is the other way around. The water is being deionized by pushing it under pressure (greater than the naturally occurring osmotic pressure) through a semi-permeable Reverse Osmosis Membrane. Therefore, a reverse osmosis filter is a water purification system that filters out a selected number of water contaminants, which will depend on their sizes. RO filters are relatively new, but have become enormously popular because of their being efficient in cleaning water. They run on water pressure, but you will need electricity (or battery) for the “pushing.”
As mentioned above, a reverse osmosis water filter is a water purifier. It removes dissolved inorganic solids (such as salts) from the water, leaving almost all of them (around 99%) behind in the reject (also called concentrate) stream. The semi-permeable membrane allows only the water to pass through, and the water contaminants and impurities are being flushed down the drain. With this principle, you will need an RO system if you are living in a hard-water area, or when you have to use underground water.
To increase the “push” (adding pressure on the salt side of the reverse osmosis system), a high-pressure pump is needed. The required amount of pressure depends on the salt concentration of the feed water. Therefore, more pressure is needed if the feed water has more concentration. In most cases, any contaminant that has a molecular weight more than 200 is likely to be drained. Carbon dioxide (CO2) has a very low molecular weight, which is why it is not being removed in the RO process.
Choosing the best reverse osmosis system depends on a lot of factors. But first, you need to understand that most of them have the same parts. If you will buy a standard reverse osmosis water filter system, it would have the following: Cold water supply valve, Automatic Shut Off Valve (SOV), check valve, pre and post filters, flow restrictor, storage tank, faucet, drain line, and the Membrane, which is the heart of the system. However, there are also tankless RO systems.
There are two types of reverse osmosis membranes – the CTA (cellulose triacetate) membrane and the TFC (thin film composite) membrane. RO systems that use CTA membrane are usually found in municipal (or city) water systems, while those that use TFC membrane are more popular in both municipal and well water systems. Generally speaking, CTA-based systems are cheaper than the TFC-based, but they tend to produce lower quality and volume of purified water.
RO filter systems also differ on how they are installed. Some of them also have different number of stages of filtration processes; each stage is designed to remove specific kinds of contaminants. The higher the number of stages is, the slower the filtering process. And beware, RO filter system with higher number of stages does not necessarily mean they produce cleanlier water. Some of these stages may be designed only to protect the RO membrane, not to increase the quality of water.
As the name suggests, this system is placed under the kitchen or bathroom sink. A huge advantage of under sink RO filters is that they have very little amount of wasted water. They also last long, and therefore a good money saver in terms of filter replacements. Water flow is also comparatively faster than faucet-mount filters, and the quality of water is high. However, you will need a professional plumber for the installation. And because the filters are heavy, they make break or leak over time, especially if you buy a low-quality, cheap RO filter system.
Just like under-sink reverse osmosis filter systems, countertop RO filters also filter lots of water. However, they are a bit cheaper and do not require professional plumbing modifications. Installation is very easy. Simply remove the aerator of your faucet, install the diverter valve and connect it to your faucet. Check for leaks and make sure there is no hot water to avoid damage of your unit. They also tend to be less likely to clog as compared to faucet-mount filters, because of its larger filtration surface. But on the negative aspect, they occupy a huge space on countertop, and they do not fit all faucets.
Below are three of the most trusted reverse osmosis filter systems in the market today:
This 5-stage iSpring 75GPD reverse osmosis system is considered one of the most efficient under-sink RO systems in the market. Its five stages start from a 5-micron sediment filter, where larger particles such as rust and dirt are being filtered. The second stage is a 5-micron GAC (Granular Activated Carbon) filter that reduces chlorine taste and odor. It is followed by a CTO (Chlorine, Taste and Odor) carbon filter. The fourth stage is where the TFC membrane is being activated, which is the most important part of the process. The fifth and last filtration stage is a finer GAC filter, or so-called final polishing filter.
Among its key features include having an Automatic Shut-Off Valve, which helps you conserve water because it automatically shuts off once the water is full. iSpring 75GPD RO filter system is also designed to produce clean drinking water at a rate of 75 gallons per day. Being a product certified by the National Sanitation Foundation (NSF) is also a great advantage. But because it is an under sink RO filter, you will need a professional plumber for the installation. And if your supply water pressure is below 45 psi, you will be required to buy a booster pump. Nonetheless, the price is reasonable enough.
The Watts WP5-50 Premier reverse osmosis water filter system also has five stages, and is NSF tested and certified as well. Having a manifold design is a good advantage in terms of avoiding clutter connections. You need a booster pump if your water pressure is below 45 psi. On the other hand, using a pressure regulator is recommended if your water pressure is above 85 psi. Meanwhile, the 3-gallon storage tank just fits under an average-sized sink and completely drains after drawing two gallons of water. It takes around one and a half hour to produces one gallon, which is quite slow.
One major disadvantage of this Watts WP5-50 RO system is it is quite noisy. The hissing sound is being produced by the “air gap faucet” during filtering. In addition, the faucet is made of chromed plastic, which means it is likely to leak sooner or later, and may not be durable enough for long term use. But other than that, the unit requires very minimal maintenance. For basic troubleshooting, Watts Premier has a long list of repair techniques on their official website. But overall, the water tastes great. Installation is easy, but if you have no experience in plumbing, you should ask a professional to help you.
This New Wave Enviro Water Filter System has 10 impressive filtering stages, which you can rarely find in a reverse osmosis water filter system. Unlike other multi-stage RO systems where some stages are not for filtering processes, each stage of this New Wave RO filter is dedicated to remove specific water contaminants to make sure you have cleanlier, healthier, and odorless drinking water. But contrary to what you might think, you can easily install it by yourself; no professional help need. However, no wrench is included in the package, which you may need when you replace filters.
Each filter is designed to produce around 1,500 gallons of water before replacement. This is almost equivalent to a one year use if your family has four members. Replacement parts are readily available. Unfortunately, New Wave Enviro currently does not support varying depths of sprayer faucet aerators. You have to buy exclusive conversion kits, which are sold separately. Lightweight at 4.1 pounds, the unit is compact and therefore ideal for countertop. This product is also supported by an unconditional 30 days money back guarantee. As for the price, this New Wave RO filter is definitely a good investment.