Reverse Osmosis (RO) Information
How Reverse Osmosis Works
Reverse Osmosis is a process by which water flows to a membrane and two things happen:
- Water passes through the membrane (this water is called "permeate") and goes to a pressurized storage tank that usually holds about 2 gallons.
- Dissolved minerals and other impurities are rejected by the membrane and flow to the drain (this is called the "concentrate" or "reject" water).
When you open the faucet for purified water, the pressure tank delivers the water to you.
The best RO systems have a couple of other filters as well to protect the membrane and enhance the purity of the water. In such systems water goes through this process:
- First, raw (untreated) water goes through a 5 micron pre-filter
- Next, it goes through a granular carbon pre-filter
- Then, it goes through the membrane where it is divided into permeate and concentrate.
- Lastly, the permeate in the storage tank, when called for by opening the faucet, goes through a final block carbon post-filter on its way to the faucet.
Some RO systems also run the permeate through a "prolonged contact carbon filter" before going to the storage tank.
Not all RO systems have 4 filters in addition to the membrane. Many systems combine the tasks of these filters into 2 filters, one before the membrane and the other after. Which one you need depends on the quality of your raw water, the level of purity and protection you desire and your budget.
Depending on the incoming water pressure and other water quality parameters, it is sometimes required to have a booster pump prior to the RO.
Doesn't RO Waste A Lot of Water?
Typical Reverse Osmosis units at a kitchen sink do use more water than they produce but this is a requirement for producing the high quality of RO water. The ratio is usually about 3:1 or 4:1 reject water to product water. If a typical family of 4 uses 2 gallons of water per day, only about 10 gallons is "wasted." This is equivalent to an extra 4 minutes in the shower or an extra 1-2 minutes of a lawn sprinkler system. It's a small price to pay for the high quality of RO drinking water.
Installation
RO systems are relatively easy to install. They require a hole in the sink top for the faucet (either 1-1/4" or 1-3/8"), a supply hookup to the untreated (raw) water, a hookup to the drain for the rejected (concentrate) water, and space for a storage tank (9" round by 22" high).
Maintenance
Reverse Osmosis units require annual servicing. This is important in order to protect and prolong the life of the membrane as well as to keep the unit sanitized. This service includes:
- Filter cartridge replacement
- Testing membrane performance
- Re-pressurizing the storage tank (if necessary)
- Sanitizing the storage tank
- Flushing the membrane
- Checking the shut off valve (a valve to protect backflow of the concentrate into the membrane)
If you are having trouble with your RO unit, please contact us. We can help you troubleshoot the problem and we carry parts for most RO units.
To see a typical procedure description for maintaining an RO unit go here.
Final Point
We highly recommend inclusion of a monitor with each RO unit. This allows the homeowner to know whether the system is performing correctly and producing high quality water. Many RO units that haven't been properly cared for are not producing the quality that is expected. A monitor is a convenient way to know that your RO unit is performing as it should. The alternative is to have your RO water tested at least every 3-6 months. A monitor can either be a hand-held device or an automatic indicator at the base of the faucet that constantly checks the water.
Products We Sell
Go to the RO Products page to see the types of RO systems we typically sell.
Whole House Reverse Osmosis
All of the above pertains mostly to small drinking water units. There are some areas in the Boulder region where the well water is of such poor quality that at whole house system is required. This is a system on a much larger scale with better "recovery" rates (less reject water). There are some advantages of a whole house RO system vs. a softener and other equipment including reducing the amount of salt put back in the environment. Please contact us if you are considering this option.
