Does Reverse Osmosis Remove Iron?

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Reverse osmosis systems can remove virtually all total dissolved solids (TDS) in water, so in theory, they should be able to remove iron.

But should you use an RO system for iron reduction? And does reverse osmosis remove iron?

We’ve answered these questions in this guide.

📌 Key Takeaways:

  • Reverse osmosis systems can remove up to 99% of dissolved iron in water, making them a highly effective iron removal system.
  • However, we don’t recommend using a reverse osmosis water filter if you have more than 3 PPM of iron, because high iron concentrations can damage the membrane.
  • The best dedicated iron filter is an oxidation filtration system, which can remove up to 15 PPM of iron – or more.

🚰 Does A Reverse Osmosis System Remove Iron?

Yes, a reverse osmosis filter can remove iron from water.

RO systems are capable of removing almost all total dissolved solids in a solution. Since iron is a dissolved solid, it can be removed by RO.

However, that doesn’t mean that reverse osmosis filters are the best solution for removing iron. We’ve discussed this in more detail later in the guide.

Getting filtered water from an RO system

Does RO Remove Ferric Iron Or Ferrous Iron?

So, what type of iron can RO remove – ferric or ferrous iron?

Ferric iron is known as “red water iron”, and is oxidized iron that colors your water and causes floating rust particles. The sediment filter stage of an RO system should reduce this type of iron.

Ferrous iron is “clear water iron”, and is dissolved iron that doesn’t show up in your water supply until it comes into contact with air and oxidizes. The membrane stage of an RO system should remove this iron type.

So, in short, both types of iron can be removed by an RO system.

🔎 How Does Reverse Osmosis Remove Iron?

Reverse osmosis removes iron with a process known as membrane separation. This takes place in a semipermeable membrane:

  1. Water is forced at a high pressure through the sediment and carbon filter cartridges before reaching the membrane.
  2. Once at the membrane, water particles are forced through the membrane’s tiny pores (around 0.0001 microns).
  3. The majority of dissolved impurities – including iron – are larger than water particles, so they’re unable to pass through the pores and rebound off the membrane.
  4. These impurities are flushed down a drain along with a small amount of wastewater.

The membrane separation process continues while your drinking water faucet is switched on and the RO system is in use, providing you with a consistent supply of purified tap water.

Related: Does reverse osmosis remove manganese?

Illustration of the reverse osmosis membrane
How the RO Membrane Filters Contaminants from Water

📊 How Much Iron Can A Reverse Osmosis System Remove?

When used to treat low levels of iron, a reverse osmosis system can remove up to 99% of all iron present.

That means the iron in your water should be greatly reduced, if not eliminated, by the time it leaves your faucet.

There are a few factors that affect how much iron an RO water filter can remove:

  • The age of the system – older membranes may not be quite as effective at removing dissolved contaminants.
  • The amount of iron – the more iron in your water, the higher the likelihood of some particles being able to slip through the membrane.
  • The other contaminants in your water – other contaminants present in your drinking water supply might interfere with the membrane’s ability to reduce iron.
  • The type of iron – certain types of iron are easier to remove with filtration than others. For instance, iron bacteria will simply clog the system.

🤔 Should You Use A Reverse Osmosis Filter For Iron Removal?

We think reverse osmosis is a good iron removal method if you have a low iron concentration in your drinking water.

However, we don’t recommend using RO water filters if your water contains more than 3 PPM of iron. Excess iron in your water will foul the membrane, causing clogging and reducing its surface area, which in turn will reduce its efficiency.

Plus, unless you want to spend upwards of $4,000 on a system, you won’t be able to use RO to protect your entire home’s plumbing system from iron.

Most RO filters are installed as point-of-use units, such as under-sink or countertop units, connected to your kitchen faucet. That means they purify your tap water, but they won’t prevent iron staining in your pipes, plumbing fixtures, water heaters, and appliances.

There are better water treatment methods for removing iron, including dedicated iron filters, that are ideally equipped for removing this mineral from your drinking water. These iron filters can remove all types of iron, including organic iron and even (in some cases) iron bacteria.

We’ve shared our top recommendations for iron water filters at the bottom of this guide.

Discoloration of reverse osmosis membrane

📋 Effects Of Iron On RO Membrane

How exactly does iron affect the semipermeable membrane in an RO system?

You probably know first-hand of iron’s staining abilities. Iron stains the surfaces it comes into contact with, especially if it’s oxidized.

Over time, high concentrations of iron minerals will build up on the membrane surface, in the same way that they do in your sinks, toilets, and other fixtures.

This blocks the membrane pores and reduces the volume of water particles passing through. As a result, more water rebounds into the RO chamber and is flushed down the drain, meaning a higher volume of water is wasted per gallon of purified water produced.

Iron fouling may even damage the membrane to the extent that holes form in its surface, allowing contaminants to pass through and reducing the system’s purification abilities.

A semi-permeable membrane is supposed to last 2 years, but if your drinking water has a high iron concentration, you might need to replace it within half of this time – or even earlier.

📝 Good Alternative Methods Of Iron Removal

So, we now know that RO systems aren’t the best method of removing iron from moderately or heavily contaminated water supplies.

The iron filters we recommend instead are:

Oxidation Filters

The very best dedicated iron filter is the oxidation & filtration system.

There are a few different types of this system:

  • Air injection systems, which send water through an air bubble to oxidize the iron, before removing it with a filter media.
  • Chemical injection systems, which inject chemicals (like chlorine or ozone) into the water to oxidize the iron, before removing it with a filter media.
  • Media-only systems, which use a filter media that can both oxidize and filter out the iron, such as manganese greensand.

Oxidation & filtration water treatment is the best way to remove iron and other common, naturally occurring metals from your whole home’s water supply.

These filtration systems are installed at the main water pipe’s point of entry into your home. They reduce up to 15 PPM of iron (some even more than this – up to 30 PPM), along with sulfur and manganese.

Certain types of chemical treatment systems, such as chlorine injection systems, can also reduce iron bacteria.

Water treated in an oxidation & filtration unit should be virtually free from iron, with no metallic taste and no staining around your home.

Installing the springwell WS1 whole house well water iron filtration system

Water Softeners

If you want to tackle hard water and low-to-moderate iron concentrations in your whole home, a water softener is a better alternative to an RO system.

For a start, water softeners are cheaper, with prices starting at around $800 for a decent system – while whole-home RO systems are usually $4,000+.

A water softener is also better equipped to deal with low levels of iron, and you can use a resin cleaner to reduce iron fouling.

Again, you shouldn’t use water softeners if your water’s iron levels are very high, but they’re a good solution for reducing moderate concentrations of ferrous iron (around 3-4 PPM).

Most water softeners also come with a sediment pre-filter, which can remove low levels of ferric iron.

KDF Filters

Another possible iron treatment method is KDF filtration. KDF filters are commonly found alongside sediment and carbon filters in multi-stage filtration systems, and can reduce up to 95% of iron with a water treatment process called oxidation-reduction.

You can use a KDF filter to effectively reduce iron if your water contains around 4-6 PPM of this mineral.

High levels of iron may clog the filter, and make sure to do your research because only certain types of KDF filters can reduce iron.

Springwell cf whole house water filter catalytic carbon and kds media

📑 Final Word

RO filtration systems work fine if your water contains low iron levels and your top priority is to purify water for drinking and eliminate the metallic taste.

But they’re not the best solution if you want to protect your entire home from high levels of iron. In this case, look for whole house filters that reduce 5 PPM of iron at the very least.

Regardless of the filter type you choose for iron reduction, make sure to buy from a trusted brand with a history of positive customer feedback. Iron filters often cost upwards of $1,000, and you want your investment to be worth it.

  • Brian Campbell
    President & CEO, CWS, CWR

    Brian Campbell, a WQA Certified Water Specialist (CWS) and Certified Water Treatment Representative (CWR) with 5+ years of experience, helps homeowners navigate the world of water treatment. After honing his skills at Hach Company, he founded his business to empower homeowners with the knowledge and tools to achieve safe, healthy water. Brian's tested countless devices, from simple pitchers to complex systems, helping his readers find the perfect fit for their unique needs.

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