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    What Is Reverse Osmosis?

    Quickly find answers to some of our most-asked questions below.


    What Is Reverse Osmosis (RO)?

    Reverse osmosis is a process that removes foreign contaminants, solid substances, large molecules and minerals from water by using pressure to push it through specialized membranes. It is a water purification system used to improve water for drinking, cooking and other important uses.


    How Does Reversed Osmosis (RO) Work?

    As its name implies, RO takes osmosis, a natural process that occurs in every cell-based organism—plants, animals and even people—and reverses it.

    how osmosis works

    To understand reverse osmosis, you first need to know – what is osmosis? During regular osmosis, a diluted solution passes through a semipermeable membrane and flows into a more concentrated one. Example: When your fingers become “prune-y” after swimming in the ocean. Through osmosis, the water in our bodies passes through our skin, out to the water around us.

    Now, here’s how reverse osmosis works:

    • Unlike osmosis, which is a passive process, reverse osmosis requires external force (pressure) to work.
    • Pressure is applied to a highly concentrated solute solution (e.g., salt water) to pass through a membrane to a lower concentrate solution.
    • The membrane allows water to flow through but blocks out larger molecules, like contaminants.
    • The reverse osmosis process leaves higher concentrations of solute (e.g., salt) on one side and only the solvent (e.g., fresh water) on the other.
    How Reverse Osmosis Works

    How Does A Reverse Osmosis (RO) System Work?

    Reverse osmosis is a method that can be applied to water filtration to help remove other minerals, substances, molecules and impurities from the water that runs throughout your house. RO systems vary depending on brand and design, but in general, they perform the following functions: pre-filtration, reverse osmosis, drainage and storage.

    Under-the-sink reverse osmosis drinking water system

    Here are the steps of water filtration through a reverse osmosis drinking water system:

    Step 1: Pre-Filtration

    The system connects to drinking water lines and uses a high-pressure pump to propel feed water through. Feed water passes through a series of filters, usually carbon-based, designed to “catch” sediment and mineral deposits before flowing into the reverse osmosis chamber.

    Step 2: Reverse Osmosis

    Here, the feed water is pushed through the semipermeable membrane.

    Think of the membrane as a tightly woven piece of fabric—one that looks virtually impermeable to the naked eye. To give you an idea of how stringent the membrane is, the diameter of a strand of human hair is roughly 100 microns wide. But, in Culligan RO Systems, the spaces in the membrane are approximately ONE micron wide.


    Step 3 + 4: Drainage & Storage

    The system drains out all contaminants not caught in filters at each stage, and treated water is stored in a small tank until used.

    One micron semipermeable membrane

    What Are Common Contaminants Removed By Reverse Osmosis (RO)?

    A high-performing RO system can remove up to 99% of dissolved contaminants found in feed water. These common water contaminants include:

    • Salts
    • Particles
    • Colloids: oil and fat-based molecules
    • Organic bacteria
    • Pyrogens: protein-based substances produced by bacteria that cause fevers when introduced into the human body