How Does Reverse Osmosis Filtration Work?

Reverse osmosis isn’t child’s play. It’s a highly scientific purification method that relies on chemical potential instead of traditional filtration methods.

Sounds heavy, doesn’t it?

Fortunately, it’s not overly difficult to understand. Don’t let the “chemical” part of  “chemical potential” scare you away from water that’s been purified using reverse osmosis. Reverse osmosis purifies water to an extent that many filtration systems can’t. There’s nothing added to the water to purify it—no chemicals or other treatments. Yet the process is making a huge difference in our world’s water.

Regular Osmosis

To understand reverse osmosis, you first have to understand regular osmosis. Osmosis is when a solution (like water) passes through a semipermeable membrane (like a filter), which blocks the passage of some of the solutes in the solution. And because that makes little sense on its own, let’s break it down, using saltwater as an example.

You have a U-shaped glass tube, and in the middle there’s a semipermeable membrane. You pour saltwater in one end, and freshwater in the other. Water, as a rule, loves equilibrium. So you’ll notice the level of the U-shaped beaker with the saltwater rising. This is the solution (water) trying to level itself out. The weaker solution (freshwater) moves through the semipermeable membrane toward the stronger solution (saltwater). This ultimately lowers the concentration of salt in the saltwater solution, leveling everything out as best it can. And that is regular osmosis.

Regular Osmosis

Reverse Osmosis

When you reverse the process, you’re forcing the higher concentration into the lower concentration—the reverse of what the solutions want to do naturally.

Same scenario: U-shaped tube, semipermeable membrane in the middle, saltwater on the left side, freshwater on the right. But instead of letting the freshwater work its way over to the saltwater, you apply pressure to the saltwater side, forcing it (against its will) into the freshwater. The semipermeable membrane acts as a filter—it captures the solute (the salt) while it lets the solvent (the water) pass through into the fresh water. The salt molecules are larger than those of the water molecules, making it possible.

Reverse Osmosis


The reverse osmosis process desalinates water, like in the example above. Scientists are using the process to turn seawater into fresh water for drinking and other uses. Not only salt, reverse osmosis purification can remove many other impurities from water as well, including fluoride, iron, and calcium.

The process is even used to make maple syrup.


Reverse osmosis kits can be purchased for your home, but they’re going to be more expensive than a traditional charcoal filter. Unless you’re performing a lot of surgeries or you live in an area with tainted groundwater, a reverse osmosis system probably isn’t a necessity for your home, but it can provide you with additional peace of mind in regard to the water that you’re putting into your body.

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