What Does Reverse Osmosis Do? - Wisler Plumbing & Air

I think most people who hear the word osmosis think of plants absorbing water. But we’re talking about reverse osmosis today, which is generally referred to in RO drinking water or RO treatment. Reverse osmosis treatment is a way to purify food-grade water for cooking and drinking. It’s generally done at the point of use (e.g., the kitchen sink). One thing to remember about RO is that it takes good water to make great water. If really bad water was put through reverse osmosis, the filter would get plugged up very quickly.

Reverse osmosis is a pretty extensive process, with four different stages of filtration. Water first goes through a pre-filter to remove any sediment particles large enough to get trapped. After traveling through the filter, the water goes through the reverse osmosis membrane. In layman’s terms, the membrane is a piece of plastic that the water runs through. Any contaminants or larger particles will get caught in the membrane and might cause it to get stopped up. To get the water to go through the plastic, it has to have enough pressure and be at the right temperature. The hotter the water is, the easier it will go through the plastic. Higher pressure helps too, but is limited because the membrane is extremely fine.

If you run a gallon of water through an RO system, it will produce about a half gallon of drinking water. Basically, this means that 50% of the water is wasted. The other half gallon of water is actually used to rinse the membrane and keep contaminants from stopping it up. (This water goes down the drain.) The amount of wasted water isn’t anything to be alarmed about, though. It doesn’t really add up to a ton because a person will generally only drink a gallon or so every day. After the filtered water leaves the membrane, it goes into two different post-filters that use carbon to polish the water. The purpose of this step is to improve the taste of the water and make it as attractive as possible for drinking and food-grade purposes.

Because of the 50:100 ratio of usable water, it takes a little bit of time for the RO filtration to do its job. There’s usually a 2 gallon storage tank that’s part of the system so you’ll have plenty of water immediately available for use. Sometimes overnight or whenever you use a lot of water, the system will kick in, start making more water, and reserve it in this tank. The storage tank easily fits right under the sink because it’s only about 12” tall and 10” around. But since it does take up some space, we might be able to put the system elsewhere and just run a little tube to the sink. (This really depends on the house. There needs to be a place where we have access to run the little plastic tube.) In my house, the reverse osmosis system is located in my mechanical area in the basement instead of under the sink.

There are three different levels of water: utility grade water that’s useful only for pressure washing or car washing, laundry grade water that won’t stain fixtures, and then food-grade water that’s only used for drinking and cooking. It doesn’t make sense to put food grade water throughout the entire house. Not only would that be really expensive, but it is corrosive and not suitable for whole-home use.

To learn more about using reverse osmosis in your home, contact us online or give us a call at 540-483-9382.