Does Reverse Osmosis Remove Salt?

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When it comes to water treatment, reverse osmosis is king. There are very few water filters that can remove as many contaminants as an RO membrane, and virtually none that can purify water in the way that reverse osmosis can.

But can reverse osmosis remove salt? The answer is yes – reverse osmosis systems are capable of removing salt.

In this guide, we’ll be sharing more about the reverse osmosis process and how an RO system can remove sodium ions.

⚗️ How does Reverse Osmosis Work to Remove Salt?

A reverse osmosis system is a multi-stage water filter system that usually consists of:

  • A sediment pre-filter
  • A carbon filter
  • A reverse osmosis membrane
  • A post, or polishing, filter
  • (Optional) a remineralization filter

Water flows through the system, and each filter stage removes a different set of contaminants. The sediment filter removes sediment, the carbon filter removes chlorine, and the polishing filter removes lingering contaminants.

These filter stages alone can’t remove tiny particles, such as dissolved salts. That’s where the semi-permeable membrane comes in. This membrane has a pore size of about 0.0001 microns – meaning that any contaminants smaller than this are blocked.

Dissolved salt is typically small enough to slip through a sediment filter, and isn’t adsorbed by activated carbon – but it’s too big to pass through a RO membrane.

As a result, while water particles pass through the membrane, sodium ions and other contaminants rebound off the membrane and become trapped in the RO chamber. These contaminants are then flushed down the drain with a small amount of wastewater.

Reverse osmosis membrane filter process

📤 How much Salt does Reverse Osmosis Remove?

Reverse osmosis systems are capable of removing more than 99% of salt from water. The RO process can remove most types of salt from drinking water, including water softener salt, table salt, and sea salt.

In fact, reverse osmosis is so effective at removing salt that it’s most commonly used for purifying seawater, making it safe to drink in a process known as desalination.

🧫 Other Contaminants that Reverse Osmosis can Remove

Reverse osmosis doesn’t only remove salt – it also removes more than 99.9% of all total dissolved solids (TDS for short).

What are total dissolved solids? Essentially, any dissolved organic or inorganic substance is classed as a TDS. Examples of total dissolved solids are chlorides, sulfates, calcium, magnesium, sodium, potassium, and bicarbonates.

The great thing about reverse osmosis is that a single system can remove or reduce so many common drinking water contaminants, including:

  • Chlorine and chloramine
  • Heavy metals like copper and lead
  • Arsenic
  • Fluoride
  • Nitrate
  • Potassium
  • Magnesium and calcium
  • Protozoans, bacteria, and some viruses

Most drinking water treatment systems can only remove a handful of these contaminants. A reverse osmosis system is one of the most capable water filters on the market.

Removing dangerous impurities

📝 Other Filtration Methods that Remove Salt from Water

While an RO system is the best way to remove sodium chloride from drinking water, it isn’t the only option.

Some of the other methods that can reduce salt in municipal water supplies are:


Distillation produces pure water by boiling water until it evaporates, leaving all impurities behind.

During distillation, water is boiled until it turns into water vapor. This vapor travels along a cooling corridor and condenses into a separate container. Most contaminants, including salt, don’t have the same boiling point as water, so they remain in the boiling chamber.

Distillation is another highly effective water purification method. However, a distiller takes much longer than a reverse osmosis system to produce pure water. While an RO system takes just seconds to treat water, distillation takes hours – up to five hours, in fact, to produce a single batch of clean water.

Distillation Process

Ion Exchange

If you own a water softener, you should know that salt can be added to water in the ion exchange process. So, it makes sense that salt can also be removed by ion exchange systems and replaced with a more favorable ion.

In most cases, sodium chloride is exchanged for calcium hydroxide. This method isn’t ideal if the reason your water contains salt is because you’ve installed a water softener, as you’ll essentially reverse the water softener’s effects. Ion exchange salt removal is usually only used for the treatment of seawater.

🤔 Can a Water Filter Remove Salt?

You might be wondering whether a standard water filter, such as a water pitcher filter or an under-sink filtration system, can remove salt from water.

The answer is no – not typically. Dissolved salt is particularly challenging to remove from water. It can’t be removed by processes like adsorption, and it’s small enough to slip through the pores of most mechanical filters.

Even ultrafiltration, the most similar process to reverse osmosis, retains beneficial minerals and salts – so it doesn’t reduce sodium.

Some microfilters that are designed to remove tiny contaminants like bacteria and viruses may reduce sodium levels, but they shouldn’t be relied upon to remove all salt from water.

Under-sink and pitcher water filters

📰 How to Minimize Salt Consumption

If you’re keen to reduce your salt intake, there are other ways to reduce your sodium intake aside from filtering it out of your water:

  • Snack healthy. Choose snacks like carrot sticks or fruit in place of high-sodium chips and nuts.
  • Compare nutrition labels. When you’re grocery shopping, compare the nutrition labels of products like breakfast cereal and pizza, and choose the product with the lowest salt.
  • Cook from scratch. It can be tempting to opt for a quick frozen meal after a busy day, but cooking from scratch with raw, natural ingredients will massively reduce the salt content in your meals.
  • Watch out for hidden salt. All sorts of everyday products are packed with hidden salts, from tinned veggies to table sauces. Try to swap these out for lower-salt alternatives where you can.
  • Use salt replacements. When you’re cooking, try flavorful alternatives to salt, like garlic or onion powder, black pepper, and paprika.
  • Make smart eating-out choices. When you’re eating out, avoid foods with toppings such as bacon, pepperoni, cheese, and sauces, which are often high in salt.

Remember that humans do need salt to survive (about 500 mg of sodium a day), so you shouldn’t try to completely eliminate salt from your diet.

🧠 Reverse Osmosis Salt Removal: FAQs

How does salt get into water?

There are a number of ways that salt can get into tap water, including through industrial or agricultural waste and drainage, or seawater entering rivers, lakes, and reservoirs.

Salt can also be added to drinking water by a water softener. To produce softened water, a water softener adds a special type of softening salt to water, exchanging this salt for calcium carbonate and magnesium ions that are responsible for scale formation.

How much salt should drinking water contain?

There is no official drinking water standard for salt, but federal and state agencies advise that salt levels are lower than 20 mg/L in tap water, and most municipalities stick to this recommendation. Your water shouldn’t contain enough salt to taste salty.

Can you install a reverse osmosis system after a water softener?

Yes. If you’ve installed a salt-based water softener that uses a brine solution to exchange hardness minerals with sodium ions, you can remove this sodium downstream of the water softening system using a reverse osmosis system. This won’t reverse the effects of the water softener – you’ll still have soft water, but it will no longer contain hardness minerals or sodium ions.

What is not removed by reverse osmosis?

A reverse osmosis filter can remove virtually all drinking water contaminants – but there are a few that are able to pass through the semipermeable membrane. Dissolved gases like methane and carbon dioxide, some bacterial microorganisms, chlorine byproducts, and some pesticides and herbicides aren’t removed by RO.

What happens to salt water in reverse osmosis?

In an RO drinking water system, water is forced through a semipermeable membrane at a high pressure, which separates the salt from the water. RO can remove more than 99% of salt from drinking water.

Does bottled water contain salt?

Yes, most bottled water products contain low levels of salt. However, this depends on how the water has been treated. RO bottled water should contain only a small amount of salt, or none at all. Water from a natural source, like a spring, is likely to contain low levels of salt, and minerals like calcium and magnesium.

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