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What Is Reverse Osmosis And How Does It Work?

What Is Reverse Osmosis And How Does It Work?


  • What is reverse osmosis or what is RO and how does it work?
  • What are the stages of reverse osmosis?
  • What are the pros and cons of reverse osmosis?

If you’ve ever wondered about the process of reverse osmosis and how does it works, you’re not alone. Many of us heard about it like filtered/bottled water, but the details remain unclear.

Reverse osmosis (RO) stands up for water purification as an important part of providing clean and safe drinking water. It contains a proper science of water filter stages and installation.

In this guide Planet Ark will jump into the details of what is reverse osmosis along with how it works?

What is Reverse Osmosis? Comprehensive Guide

Reverse Osmosis, often called RO, is a method used to purify water by passing it through a semi-permeable membrane under pressure. The objective is to remove impurities, contaminants, and particles, leaving behind clean and pure water.

RO uses a synthetic lining, acting as a semi-permeable membrane, to filter out unwanted particles. This includes substances like chlorine, salt, and dirt. It goes a step further by removing microorganisms, ensuring that the water is clean down to a molecular level, leaving only pure H2O behind.

Remember the long question in exam “what is reverse osmosis and how does it work” or a longer chapter in the book of science and struggling to get good grades in exams?

How Does Reverse Osmosis Work?

The process involves using high-pressure pumps to push water through a semipermeable membrane in an RO system. This efficient water treatment method relies on varying pressure levels based on the contaminants present in the feed water.

The purified water, free of dissolved solids, is known as permeate or product water. The remaining concentrated contaminants in the brine are termed reject water and are discharged. Top-quality membranes can eliminate up to 99% of dissolved solids.

The cross-flow filtration method distinguishes reverse osmosis from conventional methods, ensuring a longer system lifespan and reduced membrane cleaning needs. The rejected stream can be recycled for water conservation.

In the initial stage of the RO system, water undergoes prefiltration. This typically involves a sediment filter and a carbon filter to eliminate sediment and chlorine that could potentially obstruct or harm the RO membrane.

Subsequently, water passes through the reverse osmosis membrane, where even particles too minuscule to be discerned with an electron microscope are removed.

Following filtration, water proceeds to the storage tank, where it is retained until needed. The RO system continues to filter water until the storage tank reaches full capacity, at which point it automatically shuts off.

When you activate your drinking water faucet, water flows out from the storage tank through an additional postfilter. This postfilter refines the drinking water further before it reaches your faucet.

Stages in the Reverse Osmosis (RO) System

What is reverse osmosis can be more understandable after knowing the stages of RO system.

The central component of a reverse osmosis system is the RO membrane; however, these systems also encompass additional filtration stages.

In every reverse osmosis water system, there is a sediment filter and a carbon filter alongside the RO membrane. These filters are referred to as either pre-filters or post-filters depending on whether water passes through them before or after traversing the membrane.

Various types of systems may include one or more of the following filters:

  • Sediment filter: Effectively diminishes particles like dirt, dust, and rust.
  • Carbon filter: Reduces volatile organic compounds (VOCs), chlorine, and other contaminants responsible for unpleasant taste or odor in water.
  • Semipermeable membrane: Eliminates up to 98% of total dissolved solids (TDS).

Below are the detailed reverse osmosis stages:

Pre-Chlorination Dosing System: Recommended for water with traces of heavy metals or contaminants, chlorine changes dissolved heavy metals to a physical form for effective filtration.

Raw Water Storage Tank: A large tank stores contaminated water to prevent pump damage due to insufficient feed water.

Feed Water Pump: Provides initial pressure for the treatment system, ensuring adequate water pressure for pretreatment and RO membranes.

Multi-Layer or Media Filter: Targets particles that RO membranes may not purify, such as nitrates and foul odors.

Activated Carbon Filter: Reduces organic matter, bad taste, smell, and chlorine in the water.

Automatic Water Softener: Removes water hardness, calcium, and magnesium ions, especially recommended for small RO systems.

Antiscalant Chemical Dosing System: Used in larger RO systems to prevent membrane fouling.

Reverse Osmosis System: The core of the process, where water is forced through the RO membrane.

Product Water Storage Tank: Holds permeate for use, ensuring constant access to fresh water.

Post-Chlorination Dosing System: Recommended for storing permeate water, maintaining cleanliness and preventing contamination.

Product Water Pump (Re-pressurization): Repressurizes permeate water based on distance and required head, typically made of stainless steel to prevent contamination.

Product Water UV Sterilizer: Placed after the storage tank for final disinfection using post-chlorination or ultraviolet sterilization.

A reverse osmosis system effectively removes contaminants through a multi-stage process, ensuring the production of purified drinking water.

Pros of Reverse Osmosis

Reverse osmosis filters nearly all contaminants, making it one of the most effective water purification methods. RO is a comprehensive water cleaning method. It is worldwide safer option to avoid water-borne diseases, highly recommended to sensitive immune system.

It can be a safer and more eco-friendly option than relying on bottled water, reducing plastic waste.

RO is pretty useful for specific needs like cooking or aquariums. As already filtered water, it avoids germs for both human and fishes.

Cons of Reverse Osmosis

RO systems can waste huge amounts of water, sometimes three to twenty times the amount produced. Wastage of fresh water is a costly penalty as many people around the world are thriving for clean drinking water.

RO cleaning method removes healthy minerals like calcium and magnesium, potentially impacting taste and water corrosiveness.

The removal of minerals from treated water decreases its pH, making it more acidic. This acidity is not harmful to humans, but it can corrode plumbing systems, strip lead and copper from pipes, and introduce toxic metals.

Reverse osmosis process can be expensive to install and maintain, requiring professional assistance. Users’ needs to be pretty active while controlling RO and its system.

What Substances Does Reverse Osmosis Eliminate?

Reverse osmosis effectively removes chlorine, salt, PFAS, and dissolved solids like arsenic and fluoride by passing them through the RO membrane. Additionally, RO systems incorporate sediment and carbon filtration to achieve a comprehensive reduction. The carbon filters within an RO system are adept at eliminating chlorine, unpleasant tastes, and unpleasant odors, while the sediment filter efficiently removes dirt and debris.

Reverse osmosis is capable of removing:

  • Fluoride
  • Salt
  • Herbicides and pesticides
  • Heavy metals
  • VOCs
  • PFAS
  • Sediment
  • Chlorine
  • Arsenic
  • Microplastics

It’s difficult to highlight that reverse osmosis systems do not eliminate certain bacteria and viruses. If your water originates from a municipal treatment plant, it is likely microbiologically safe. While reverse osmosis may remove some bacteria, there’s a possibility of bacterial growth on the membrane, which could potentially enter your water supply. To ensure the removal of living organisms and viruses, it says to use UV disinfection.

How to Prevent Membrane Scaling in Reverse Osmosis System?

Dealing with membrane scaling in a reverse osmosis system can be effectively addressed through a couple of pretreatment strategies. Two commonly employed residential pretreatment solutions for combating membrane scaling are water softeners and scale inhibitors.

  • Water Softeners

Water softeners function by exchanging sodium or potassium ions from a brine with calcium and magnesium ions present in hard water. Often referred to as ion exchange systems due to their operational method, water softeners are best for addressing hard water issues. Although a reverse osmosis membrane can handle hard water, it significantly shortens its lifespan. Therefore, employing water softening is the most efficient way to obtain high-quality soft water from a reverse osmosis system while extending the membrane’s longevity. Water softeners also serve as a practical approach for preventing scale accumulation in residential RO systems.

  • Scale Inhibitors

Scale inhibitors are chemical additives to the feed water supplied to an RO system. These chemicals enhance the water’s ability to dissolve inorganic compounds, enabling the system to operate at a higher production rate. Particularly effective against two prevalent inorganic salts in water, namely calcium carbonate and calcium sulfate, scale inhibitors exhibit versatility across a broad pH range. They are safe to handle and use, providing an excellent means of preventing scale buildup. When using a scale inhibitor, it’s important to ensure that the feed water has low levels of iron, a common contaminant in well water, to avoid compromising the inhibitor’s effectiveness.


Understanding “what is reverse osmosis” doesn’t have to be tricky. Whether you’re curious about how bottled water works or thinking about getting a water filter for your home, knowing the basics of reverse osmosis can help you make smart choices about your water.

In simple terms, reverse osmosis is like a superhero for clean water as making sure your water is pure and safe. Think of it as a special process that uses pressure to clean out all the stuff you don’t want in your water.

So, whether you’re sipping a glass of water at home or wondering about the water in your favorite drinks, remember that reverse osmosis is the background working force. We hope to provide with all basics of what is reverse osmosis and how does it work, do share your comments and let us know.

Cheers to a brighter, cleaner future for our most important resource – water!

Tap to our website and get more sustainable water-cleaning solutions.


Is reverse osmosis a better option than regular drinking water?

While it offers a comprehensive purification process, opinions on its preference may vary among individuals.

What constitutes the healthiest choice for drinking water?

Optimal health associates with consuming pure and clean water from a trustworthy source, whether it be tap or filtered. The healthiest water often includes alkaline and mineral water varieties.

Is drinking reverse osmosis water a healthy practice?

Certainly, it is safe to drink and is often purer than tap water.

What are some examples of reverse osmosis?

Reverse osmosis (RO) finds widespread application in various industries, such as home water filtration systems, aquariums, juice production, dairy products, and pharmaceuticals. It serves to eliminate impurities and contaminants from tap water, create a suitable environment for fish, and eliminate bacteria and brine from meat and alcohol. Additionally, it employs in the dairy, starch, and sugar industries, where pressurized filtration is use to remove impurities from contaminated water.

Which bottled waters utilize reverse osmosis?

Brands like Nestle, Pure-Life, Smart Water, Aquafina, and Dasani incorporate reverse osmosis in their filtration processes.

Can you explain the reverse osmosis process for drinking water?

The process entails pushing water through a semi-permeable membrane to filter out impurities.

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