What is Reverse Osmosis Water Filtration?

Under-the-counter reverse osmosis systems are plumbed to the incoming coldwater line, drain, and an independent faucet. But it is possible for a water treatment professional to plumb an RO unit to your fridge and/or ice machine, as well.

The water professional will most likely run a quarter-inch tube from the under-sink RO unit to your fridge. Water pressure is a consideration with some refrigerators, so be sure to refer to your RO system’s owner’s manual as the pressure from the reverse osmosis unit is about two-thirds of the incoming line pressure.

The typical under-counter reverse osmosis tank is 12 inches in diameter and 15 inches tall. The reverse osmosis system will operate under water pressure ranging from 40-100 PSI and generate 10-75 gallons (that is 45-340 Liters) per day.

Generally, reverse osmosis systems are very quiet-- though you may hear a “gurgling” sound as the “concentrate” or waste water flows from the membrane to the drain. Reverse osmosis is designed so that “crossflow” water flushes the contaminated concentrate away from the system. This flushing keeps the unit from fouling.

If you hear other sounds, such as a “hissing” noise, immediately call your local water treatment professional as there may be a problem with water pressure, the air gap or a leak.

Non-air gap faucets tend to be quieter than air-gap faucets. Non-air gap faucets make no gurgling sound since the drain line from the RO membrane flows directly into the sink drain line. Learn more about the difference between “Air Gap” and “Non-Air Gap” faucets.

An under sink RO drinking water filtration system uses the same technology that major water bottling plants use to filter water.

Reverse Osmosis incorporates carbon filtration which removes chlorine, chloramines, forever chemicals like PFOS, Arsenic V, pesticides, herbicides and more. The removal of these contaminants not only makes for safer drinking water, but also greatly improves the taste.

The RO process leaves trace amounts of minerals and salts which makes for an overall better taste rather than the “flat” taste of distilled or bottled water. Best of all, RO-filtered water saves you the expense of bottled water and is better for the environment since you’re not adding water bottles to local landfill. This eco-friendly solution means you can have healthy, naturally-fresh drinking water available right at your kitchen tap.

Absolutely. Looking at cost alone, RO systems generally cost less than 30-cents per day to own and operate for a family of four. From a cost-savings perspective, since most Americans spend $100/year on bottled water translating to $400/year for the household, an RO system would save nearly $300/year as it operates for roughly $100/year. And the number crunching doesn’t reveal anything about the health benefits of RO.

RO systems can remove harmful contaminants such as pesticides, PFAS, herbicides, chlorine, chloramine, and Arsenic V, certainly making an RO system “worth it.”

A whole-house Reverse Osmosis system (also called a POE “point of entry” system) allows RO filtered water at all sinks, showers and appliances throughout the house. A POE system ties into the main water line coming into your home and is generally installed in the garage.

In theory, whole house reverse osmosis systems sound like a good idea. But here are the reasons we don't typically recommend whole house RO water filters:

1. Whole-house reverse osmosis water filters can be expensive
2. Whole-house RO water filter systems require a lot of maintenance.
3. Whole-house reverse osmosis consumes a lot of water
4. Whole-house RO flushes a lot of filtered water down the drain.
5. Additional pre-treatment and post treatment will probably be needed.
6. A lot of storage space is required for the large whole-house RO system.

For more information about whole-house reverse osmosis and what whole house water filters we recommend, please read this article.

General performance data is available below for under-counter RO systems. Manufacturers often provide specific information on their system to help consumers understand the capabilities and effectiveness of their reverse osmosis system.