Reverse Osmosis Explained

Reverse osmosis offers to provide the cleanest water available. Are there any down sides to the RO process?

By: Kelsey Royer

Reverse Osmosis (RO) is a popular method utilized in recycling and wastewater treatment, as well as consumer water filtration systems. It was back in the 1950’s that scientists first considered the use of RO to desalinate ocean water, and although it worked, it was not practical due to the small volume produced. This changed when two UCLA scientists created hand-cast membranes made from cellular acetate, allowing larger quantities of water to move through the RO process more efficiently. In 1965, the first commercial RO desalination plant began running a small scale operation in Coalinga, California.

With a membrane that captures even the smallest particles, reverse osmosis is pretty amazing filtration technology. Considered one of the best by the United States Environmental Protection Agency, and shown to positively impact health, this technology is being implemented all over the world. From residential homes to large-scale plants filtering millions of gallons per day, RO is at the forefront of clean water. Take a look behind the scenes.

How does reverse osmosis work?

Osmosis, without the reversal part of the equation, is when a solvent of low concentrated solute solution moves through a membrane to get to the higher concentrated solution, thus weakening it.

For a visual explanation of reverse osmosis, you can check out this video by the Government of South Australia, which uses RO to desalinate water in the city of Adelaide. In the video, a water tank is displayed with a saltwater solution on one side and pure water on the other side, separated by a semi-permeable membrane. Pressure is applied to the saltwater side of the tank, counteracting the natural osmotic pressure from the pure water side, thereby pushing the saltwater through the filter. Due to the size of the salt molecules, only the smaller water molecules make it to the other side, thereby adding fresh water to the water side, and leaving the salt on the other side.

The EPA describes reverse osmosis as a process that “forces water through a semi-permeable membrane under pressure, leaving contaminants behind.” The process involves more than simply forcing water through a “screen”. RO requires a considerable amount of water pressure to overcome natural osmotic pressure and effectively remove impurities.

What contaminants does reverse osmosis remove?

Now that you know how reverse osmosis works, you may be wondering what contaminants it actually removes?

The effectiveness of each RO system varies, meaning some may actually remove more contaminants than others. The CDC notes that in general RO systems are highly effective at removing bacteria and viruses. The differences will likely come down to which chemicals they remove or reduce, and how effective they are at doing so. Aquasana’s SmartFlow™ Reverse Osmosis reduces the presence of 90 harmful contaminants including more than 99% of asbestos and cysts, 99% of lead and microplastics, 96% of chlorine and arsenic, and 90% of fluoride in addition to several other tap water hazards.It’s also important to note that many RO systems strip away too much — including healthy minerals that positively impact the taste and benefits of the water you drink. To ensure you’re getting the most out of your water, Aquasana’s Reverse Osmosis system uses remineralization technology to restore a good pH balance and retain healthy minerals.

Reverse osmosis facts

Reverse osmosis is considered the best available technology by the EPA when it comes to removing uranium, radium, and other radionuclides. It is the only type of filter capable of removing small contaminants like fluoride. The EPA states that RO filters “are effective in eliminating all disease-causing organisms and most chemical contaminants.”

"The EPA states that RO filters, 'are effective in eliminating all disease-causing organisms and most chemical contaminants.'"

A few other interesting reverse osmosis facts and ways the process is used:

  • RO water filters are gaining popularity in the foodservice industry – Many restaurants are investing in RO systems to help improve the taste of their food using the best quality water for cooking.
  • Reverse osmosis systems help car washes achieve a “spotless rinse” – Water that hasn’t been filtered can cause scaling and leave spots after a carwash, so some carwash facilities are utilizing RO systems to remove soluble salts that cause these issues so they can provide a “spotless rinse” for customers.
  • The production of maple syrup – RO is used to separate the sugary concentrate from water in the sap.
  • The dairy industry uses RO filtration to concentrate whey and milk.
  • Wastewater goes through the RO process to create something drinkable, thereby earning the nickname, “toilet to tap” which may be unappealing, but provides developing nations with the ability to produce drinkable water.

As stated above, RO also used to desalinate seawater. In Dubai, where fresh water is limited, large-scale reverse osmosis filters convert about 416 millions of gallons of seawater to fresh water every day. Dubai’s groundwater supplies only 0.5% of the city’s water – that means the other 99.5% has to come from reverse osmosis. In order to produce 416 million gallons of fresh water, the system has to pump about 2.8 billion gallons of water through it each day.


SmartFlow™ Reverse Osmosis

High-efficiency reverse osmosis system removes up to 99.99% of 90 contaminants, including fluoride, arsenic, chlorine, and lead.

Reverse osmosis benefits

Reverse osmosis filtering has been proven to have some seriously positive health benefits.

Helps reduce sodium intake

In homes that use water softeners to remove minerals from hard water, the ion exchange process that softeners use will leave you with water that’s fine for cleaning, bathing, and laundry — but not great for drinking. Basically, most water softeners replace hard minerals with sodium thus leading to a salty water taste. Using a reverse osmosis water filter enables you to enjoy the benefits of softer water without the added sodium and accompanying salty taste.

Helps prevent dementia

A classic example is this study which found that dialysis patients could prevent dementia (a comorbidity that occurred in 18 out of 258 patients) by simply using an RO filter. With no other treatment, scientists were able to improve the condition in 7 out of 9 previously exposed patients and prevent dementia in those whose water was treated from the start of the study.

Helps prevent gastrointestinal illness

Another study tracked the gastrointestinal health of 1400 families and found 14% more gastrointestinal illness in families drinking tap water than in those who were drinking water purified with reverse osmosis. The study noted that “14-40% of gastrointestinal illnesses are attributable to tap water meeting current standards and that the water distribution system appears to be partly responsible for these illnesses.”

The best reverse osmosis water filter

The best RO filters will have carefully engineered membranes that stand up to daily use. They filter for even the smallest particles and include additional steps to ensure that the water it provides is both clean and healthy.

It’s important to do the research necessary to know how many contaminants an RO water filter truly removes. The simple saying “don’t believe everything you read on the internet” goes a long way. Look for certifications like WQA, NSF, and IAPMO. A reverse osmosis system should pass NSF/ANSI Standards including Standards 42, 53, 58, and 401 – read more about NSF standards here.

Consumer RO filtration systems generally do a good job of stripping out harmful contaminants, chemicals, minerals, and salt, but in the process, also strip the water of essential minerals. There is some disagreement on this issue, with some health experts stating that the amount of minerals in water is negligible anyway, so RO systems are a great option. However, the venerable World Health Organization and many other health experts have stated that water is an important source of minerals such as calcium, magnesium, and iron, especially for people in developing countries. The best water filter system is one that removes all the harmful particulates while remineralizing the water. That assures that it not only tastes great but has the health benefits that essential minerals provide.