A water purification process, reverse osmosis (RO) uses a partially permeable membrane to separate contaminants, unwanted molecules and other particles from drinking water. It works in the following way: Pressure forces the unfiltered water (a.k.a. “feed water”) through this semipermeable membrane, filtering out the particles and creating clean drinking water. The fresh water produced is called the “permeate.” Salt water, for example, is often taken through this process to make it drinkable, where pressure forces the salt water through the semipermeable membrane, leaving the salt and excess water behind. But in most cases, RO is used as part of a larger purification system. Indeed, what’s known as a Reverse Osmosis System can be made up 3 or 4 different levels of filtration. Around the world, many household drinking water purification systems, commonly used for improving water for drinking and cooking, have a number of steps, including:

  • A sediment filter that traps particles, including rust and calcium carbonate
  • A second sediment filter with even smaller pores
  • An activated carbon filter to trap organic chemicals and chlorine (which will often degrade certain types of thin-film composite membranes – the type used in reverse osmosis).
  • A reverse osmosis filter
  • An ultraviolet lamp that used occasionally for sterilizing any microbes that may escape filtering by the reverse osmosis membrane
  • A second carbon filter to capture those chemicals not removed by the above processes.

What Does Reverse Osmosis Remove in Your Water

Reverse osmosis can remove many types of dissolved and suspended chemicals as well as some biological species (primarily bacteria) from water. Here are some contaminants and chemicals that can be removed by reverse osmosis:  

  • Salt
  • Fluoride
  • Chlorine
  • Sediment
  • Arsenic
  • Herbicides and pesticides
  • Volatile organic compounds (VOCs) – typically compounds deriving from petroleum fuels, hydraulic fluids, paint thinners, and dry-cleaning agents. 
  • Other contaminants such as mercury, E. coli, and other coliforms to a considerable extent.

Does Reverse Osmosis Harm the Environment?

As water flows through membrane, reverse osmosis systems divide it into two streams. One stream carries the filtered water to a dedicated faucet, and the other stream carries the wastewater with the concentrated contaminants (known as the brine) to the drain. Roughly 4 gallons of water goes to the drain for every gallon of drinkable, filtered water. That seems like waste. However, contrary to what you might think, the brine water isn’t all bad because given it often contains chemicals such as chlorine, which help clean the water down the drain as well.

That said, the goal of any RO system is to minimize the amount of waste water (brine) produced. One way to do that is to add a permeate pump, which can improve RO systems’ efficiency and can reduce wastewater by up to 75 percent. A few other things you can do:  

  • Use the RO “brine” water for landscaping or artificial lakes. It’s typically safe for lawns and gardens.
  • Choose a reverse osmosis system with an automatic shut off valve. The valve will stop the water flow once the storage tank is full.

How Does Reverse Osmosis Work with Water Softener Systems?

Generally, the two systems are complimentary. Reverse osmosis systems filter harmful contaminants from water, while a water softener primarily seeks to remove calcium and magnesium to “soften” hard water, helping improve everything from your skin tone to the running of your appliances. (Note: Reverse osmosis systems help soften water too, ridding the water of calcium and magnesium.) But in cases where homes have very hard water, the RO system’s membrane often wears out faster due to the increased presence of calcium and magnesium. A water softener installed before a RO system will hence remove a lot of the hard water elements and help improve the life of your RO membrane.  Conversely, an RO system can remove sodium added by the water softener.

How Drinkable Is the Water Produced by a Reverse Osmosis System?

Most bottled water is actually purified by a reverse osmosis system. So, it’s actually perfect to drink, but without all the super harmful environmental effects of plastic bottles. Reverse osmosis does remove calcium and magnesium, which are important minerals for the body to absorb in small amounts, but it also reduces harmful contaminants, which can adversely affect your health in cases of repeated exposure. This clean water will help lubricate your joints and aids in your organ function, digestion, and provide many other benefits.

How Long Do Reverse Osmosis Systems Last?

Typically, most systems function well for 10 to 15 years. The RO membrane and filters should be changed more frequently with prefilters and post filters being replaced every 6 months. And depending on the condition of your water (hardness) the RO membrane typically needs to be changed every 3 years. When we typically do installs, we’ll focus on implementing any reverse osmosis system where you need it most, in particular under the kitchen or bathroom sinks and for refrigerator lines.


We hope you found this helpful. There’s certainly a lot more detail you can learn about reverse osmosis systems, so feel free to ask us any additional questions you might have. We’re here to help. If you live in the Chicagoland area, you can get started on your path to better water by contacting us at Restore Water Systems. We’ll provide a free water quality analysis, so you can learn more about what’s in your water and what system is right for you.

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