What is reverse osmosis?
Reverse osmosis (RO) is a type of water filtration system that forces water through a thin, semipermeable membrane or filter in order to remove impurities. In homes with a reverse osmosis water system, water is pumped through the filter and separated from dissolved salts and other impurities. The RO system blocks contaminants, ultimately flushing them down the drain, and stores filtered water for future use. The result is highly purified water available for drinking, cooking and other uses in your home.
How does reverse osmosis work?
In an RO system, a high-pressure pump is used to force water molecules through a reverse osmosis filter, also known as an RO membrane. As water moves across the RO membrane, it’s divided into two streams. One carries the filtered water to your tap, and the other carries rejected pollutants and salts to the drain. The process is not unlike larger, state-of-the-art reverse osmosis desalination plants, which turn seawater into drinking water.
Reverse osmosis process
Brands may vary, but generally all reverse osmosis water systems perform pre-filtration, reverse osmosis, drainage and storage.
Reverse osmosis steps:
When water first enters an RO system, it goes through pre-filtration to get rid of sediment, contaminants and other particles that can cause bad taste and odor. It passes a particle filter, removing impurities like salt and sand, and an activated carbon filter, which traps and removes minerals, pesticides and chemicals like chlorine, mercury and copper.
- Reverse osmosis
After pre-filtration, the water undergoes reverse osmosis, where it’s forced through the semipermeable RO membrane. Here, particles even too small to be seen with an electron microscope are trapped and removed, allowing only filtered water to pass through.
Removed contaminants are flushed away in the final discharge stage with all rejected impurities carried down the drain. Because these pollutants are carried away with the brine water that initially comes into the system, they are unable to clog the RO membrane.
Meanwhile, filtered water flows to a storage tank, where it’s held until needed. Before it reaches a faucet, it undergoes a final activated carbon filtration to improve taste and quality for household use.
What does reverse osmosis remove?
Depending on the quality of your initial water source, whether it be an onsite well or municipal water line, an RO system is capable of removing up to 99.99 percent of the contaminants in your water. According to the Centers for Disease Control and Prevention (CDC), reverse osmosis systems have a high effectiveness in removing protozoa, bacteria, viruses and common chemical contaminants such as sodium, chloride, chromium and lead. The may also reduce arsenic, fluoride, radium and sulfate, among other pollutants.
Contaminants removed by reverse osmosis:
- Arsenic: 95%
- Aluminum: 97%
- Barium: 95%
- Bicarbonate: 95%
- Cadmium: 97%
- Calcium: 97%
- Chloride: 94%
- Chromium: 97%
- Copper: 98%
- Fluoride: 95%
- Iron: 98%
- Lead: 97%
- Magnesium: 97%
- Manganese: 97%
- Mercury: 97%
- Nitrate: 95%
- Potassium: 92%
- Radium: 97%
- Selenium: 97%
- Silver: 96%
- Sodium: 95%
- Sulfate: 95%
- Zinc: 98%
- 2,4-D Pesticides: 95%
- Protozoa: 99%
- Asbestos: 99%
- Trihalomethane (THM): 98%
Can you drink reverse osmosis water?
Water treated with reverse osmosis is drinkable. In areas where water has been chemically compromised, reverse osmosis systems can help remove contaminants and make it safe to drink. For example the United States military has used the process to transform salt water into fresh water for troops.
The technology does not differentiate between bad substances and good ones so nutrients the body needs wind up being eliminated along with all undesirable substances. Therefore, drinking reverse osmosis water should be coupled with a diet rich in vitamins and minerals in order to avoid deficiency.
How much is a reverse osmosis system?
Whole house RO systems average up to $10,000 or more for commercial-grade varieties. Self-installed, under-sink models range from $150 to $400 on the low end or $500 to $750 on the high end.
The specific reverse osmosis system price will depend on the sophistication of the unit. Those with multiple stages of purification will cost more. If the system contains an additional UV treatment feature or adds minerals back into the filtered water, its price tag could be over $1,000 for a home unit. Units that must be professionally installed and maintained also cost thousands of dollars.
Reverse osmosis pros and cons
A reverse osmosis system’s ability to remove lead, sodium and other contaminants make it extremely useful to individuals with weakened immune systems, high blood pressure, and kidney or liver disease. However, that same capacity to clean can also be a detriment because water filtered through reverse osmosis is stripped of body-nourishing vitamins and minerals.
Reverse osmosis benefits:
- Provides clean water
RO technology can remove 95 to 99 percent of total dissolved solids (TDS) from source water, as well as chlorine, fluoride and other impurities, greatly reducing odor and improving taste.
- Uses little to no energy
Because they use the water pressure already coming into the house, reverse osmosis systems require little to no energy to function.
- Easy to maintain
Depending on use and water quality, most filters need to be replaced once every six to 12 months, while semipermeable membranes can last two to three years. Beyond that, an RO system usually requires only annual cleaning and sterilization and has a life expectancy of 10 to 15 years.
Reverse osmosis disadvantages:
- Purification leaves water "dead"
Since the process doesn’t discriminate, good stuff is filtered out along with the bad, leaving the water pure but also “dead,” according to critics, who say it contributes to vitamin and mineral deficiencies in users.
- Process is slow
Because reverse osmosis uses household water pressure to push water through the RO membrane, the process takes time. If you need a lot of filtered water quickly and empty the system’s holding at once, it’ll take time to refill the holding tank (as much as 4 hours).
- Creates large amount of waste water
A large portion of the water that runs through the system is rejected and sent down the drain, which doesn’t bode well for the environment. Water bills may also increase as a result.