Does Reverse Osmosis Remove Salt from Water?

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Sodium is an essential mineral for humans, but excess salt in water can cause adverse health effects and even damage your plumbing.

Reverse osmosis has been touted as a solution to many water contaminants, but does it work for salt?

In this article, we’ll discuss reverse osmosis and salt (or sodium) removal and see other ways to remove salt from water.

Key Takeaways

  • Yes, reverse osmosis removes salt (sodium) from water.
  • A reverse osmosis system can remove up to 99% of salt from water.

Does Reverse Osmosis Remove Salt from Water?

First of all, does reverse osmosis remove salt from water?

Yes, reverse osmosis does remove salt from water, and it does so very effectively.

How Does Reverse Osmosis Water Purification Remove Salt?

Reverse osmosis works by forcing water through a semipermeable membrane under high pressure. An RO membrane has very tiny pores (about 0.0001 microns) that stop larger molecules from passing through it.

When feed water rushes through a reverse osmosis system, the tiny pores in the membrane block salt molecules but allow water molecules to pass through.

At the end of the filtration process, you get clean, salt-free water while the system washes the trapped salt down the drain.

Under Sink Reverse Osmosis System

How Much Salt Is Being Removed?

Reverse osmosis systems remove about 99% of salt in water, so almost all of it.

Can You Use RO to Remove Water Softener Salt?

Water softeners are devices that soften hard water. They work by replacing the hardness-causing minerals in water with sodium ions. That’s why, softened water can contain a lot of salt or sodium.

Fortunately, you can remove water softener salt from your softened water using reverse osmosis just like you would use it to remove any other sodium.

Other Contaminants Removed by Reverse Osmosis

Here are some other contaminants removed by reverse osmosis systems:

  • Protozoa, bacteria, and viruses
  • Metal ions
  • Chlorine and chloramine
  • Disinfection byproducts like HAAs
  • Fluoride
  • Nitrates
  • Sediments
  • PFAS

Generally speaking, reverse osmosis removes close to 99% of total dissolved solids (TDS) in water. TDS are particles that dissolve in water, like organic matter, bicarbonates, and most metals.

Other Water Filtration Methods That Remove Salt

Reverse osmosis may effectively remove salt from water, but it’s not the only method that works. Here are other filtration methods:


Water distillation operates with the principle of boiling, evaporation, and condensation.

Most water impurities, including sodium, have a higher boiling point than water. During distillation, water is heated until it reaches its boiling point, then it evaporates and moves into a separate chamber to cool. Since the salts and other impurities do not evaporate with the water, they stay in the boiling chamber, where you can wash them off later on.

The vaporized water condenses and settles in a new chamber, and for extra protection, the water goes through a post-filter to remove any leftover contaminants.

Distillation is a thorough and effective way to remove salt from water, but it’s really slow. A home water distiller (the device used for distillation) takes about four to six hours to purify one gallon of water.

Ion Exchange (Deionization)

First, let’s clarify that the ion exchange here differs from the usual ion exchange for water softening. Water softening replaces hard minerals with salt, while this ion exchange (also known as deionization) replaces salt ions in water with safer ions like hydroxyl or bicarbonate ions.

Deionization uses a specially designed resin made from beads of organic polymer chains. When water flows through the resin in the filter, it traps any salt ions.

How Does Salt Get into Our Water in the First Place?

When you think about it, it’s not surprising to find salt in so many water sources. Sodium is one of the most abundant elements on earth, and it never exists freely but as a compound. In most cases, this compound is sodium chloride also known as table salt.

Table salt is highly soluble, so it mixes with water very quickly. Here are four specific ways salt can enter your water supply:

Movement of Groundwater

Water comes in contact with salt deposits as it flows underground. Since salt is highly soluble, it dissolves easily into underground water. Areas with extensive underground salt deposits will find their water naturally salty.

Snow Melts

In areas with heavy snowfalls, salt is usually used to melt the snow on the roads. The salt dissolves into the melted ice, seeps into the ground, and adds to the salt content of water aquifers. If you live in such areas, you’ll have salty water.

Water Treatment Chemicals

Treating water with chemicals like sodium fluoride, sodium bicarbonate, and sodium phosphorus will increase the water’s salt level. But these chemicals don’t add too much salt in the water unless you use them all simultaneously.

Water Softeners

Water softeners replace hard minerals in water with salt ions. The EPA confirms that softeners can raise salt levels in drinking water to over 300 mg/L. But the level of salt the softener adds depends on how hard your water is. So if your water is averagely hard, a water softener will only add a little bit of salt to your water.

Water Softener Open Brine Tank with Salt

Is Sodium in Drinking Water Harmful?

Sodium is an essential mineral. It helps with nerve impulses and muscle functioning. The average adult needs about 500 mg/day of sodium to stay healthy.

However, ingesting too much sodium long-term can lead to issues like high blood pressure, heart attack, and even stroke. Consuming excess sodium can cause vomiting, convulsions, gastrointestinal issues, and death.

Since most of our daily foods and supplements already contain too much sodium, drinking water that also contains sodium could potentially lead to an overdose.

So yes, sodium can be harmful in drinking water, but only if the sodium level in your drinking water is high, and you eat a lot of sodium-rich food. The safe level of sodium in drinking water is 270 mg/L. However, people on sodium-restricted diets should not intake water that contains more than 20 mg/L.

About RO for Seawater Desalination

Seawater naturally contains high levels of salt, so it has to be desalinated before anyone can use it (desalination means having salt removed).

Good news is, reverse osmosis is an efficient, environmentally-friendly method of desalinating seawater to make it safer. Here’s how it works:

A seawater RO system contains two essential components; the feed pump and the semipermeable RO membrane. But before those components even work, pre-filters remove organic contaminants like seaweed, oil, and particles from the seawater. This pre-treatment is necessary because seawater contains a lot of sediments, which can damage the primary RO membrane.

After pre-filtering, the system pumps water through the semipermeable membrane. Here, the salt molecules are filtered out, and only pure water passes through. The clean filtered water goes through post-treatment before it’s stored and distributed for use. Finally, the obstructed salt minerals (or brine solution) are diluted and returned to the sea.

Should You Combine RO and Water Softening?

Reverse osmosis systems and water softeners work well together. Water softeners remove hardness minerals, but the downside is that they leave salt in your water. Reverse osmosis systems complement the purification process by filtering salt (and other contaminants) out of your water. That way, your water will be soft, salt-free, and without harmful pollutants.

If you’re combining both types of systems, it’s best to install the RO filter after the water softener (so the water softener comes first). This is because hardness-causing minerals can damage an RO membrane. If the softener comes first, it eliminates any hardness before the water reaches the membrane.

How to Reduce Your Daily Salt Intake

Apart from removing sodium from your drinking water, there are other effective ways to reduce your overall daily salt consumption:

  • Avoid snacks that contain sodium, like chips and nuts. Replace them with healthy fruits.
  • Check nutrition fact labels before buying cereals and other food packages. Look out for the sodium content. You should choose products with the lowest sodium content.
  • Add natural spices (like ginger, garlic, and rosemary) to your food while cooking to reduce the salt you need to add.
  • Cook for yourself more often than you eat out. Convenience meals like pizza, boxed potatoes, and frozen food often contain high sodium.
  • When buying packaged meals, choose those labeled “low-sodium”.
  • Reduce meals with toppings high in sodium, like cheese and bacon.
  • Buy fresh meals instead of frozen foods.
  • Consult a registered dietitian (you may find one at your grocery store) for tips to reduce your sodium intake and the best food products for low salt.

If you have any thoughts about the question, can reverse osmosis remove salt, please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
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