Does Reverse Osmosis Remove Limescale from Water?

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Limescale is one of the impurities that most frequently prompt people to look into water treatment.

It’s far from the only impurity found in household water, but it’s a prevalent and problematic one nevertheless.

Is reverse osmosis a good way to get rid of limescale from your water? Let’s find out!

Key Takeaways

  • Reverse osmosis is very effective at removing limescale from water. Reduction rates of 95% can be achieved.
  • However, RO membranes are prone to clogging when used on water with excessive limescale levels.

Does Reverse Osmosis Remove Limescale from Water?

Reverse osmosis is one of the most effective methods for removing limescale from water. It’s a thorough mode of filtration in general, and it gets rid of limescale easily.

However, you need to be careful. One issue with this setup is that reverse osmosis membranes tend to be affected negatively by excess limescale concentrations, and they start to clog up quickly. That’s why with whole house reverse osmosis systems in particular you often use a water softener for pre-treatment. The softener gets rid of most hardness before the water reaches the RO membrane.

If you still want to use reverse osmosis to remove limescale from your water, the process works by forcing water against a thin, semipermeable membrane at a high level of pressure. The membrane’s pores are very tiny (around 0.0001 microns in diameter), and they essentially only allow water molecules to pass through. Reverse osmosis is particularly effective at removing minerals from water. And since the main component of limescale is calcium carbonate, this makes it the perfect candidate for getting filtered out with reverse osmosis.

blue reverse osmosis membrane

How Effective Is Reverse Osmosis at Removing Limescale?

The process is close to perfect in terms of efficiency – you can expect reverse osmosis to remove as much as 95% of the limescale in your water supply. While this will still leave you with some tiny trace amounts, those will be far from enough to cause any noticeable difference in the quality of your water.

What Is Limescale?

Limescale is a deposit with a large concentration of calcium carbonate and often magnesium, which naturally builds up inside plumbing and water appliances over time. Limescale is particularly problematic for hot water appliances like washing machines and water kettles. It’s typically white-grey in color, although it can occasionally take on alternative colors when other minerals are present in the water in higher amounts.

While some people see it as a purely aesthetic issue, limescale can actually be very problematic for many appliances, shortening their lifespan and causing them to need more frequent maintenance. That’s why it’s recommended to treat your appliances for limescale buildups if you live in an area prone to them.

Where Does Limescale Come from?

Limescale is simply the result of certain minerals that are naturally present in the water evaporating and leaving a hard trace behind. Calcium and magnesium are the biggest offenders here. If you live in an area with hard water, then you’re also predisposed to limescale buildups and need to pay more attention to your water filtration.

But why are these minerals in the water in the first place? It’s just a natural result of the way water flows through the environment. When water passes through rock formations with lots of mineral deposits, some of those minerals leach into the water. Eventually, they reach your household.

Is Limescale the Same as Calcium?

No, but the presence of calcium is one prerequisite for the development of limescale. Calcium and magnesium are two of the most abundant minerals in nature, and they are often found in high concentrations in the water supplies of certain areas. Calcium’s calcite form – calcium carbonate – is the primary foundation of limescale buildups.

Other Ways to Remove Limescale from Water

While reverse osmosis is one effective way to remove limescale from water, it’s not the only option available. There are various other approaches out there – here are some of the most popular ones.

Water Softeners

Water softeners are specifically designed to remove hard water minerals. Naturally, this means that they also remove calcium and magnesium, and therefore work very well at addressing limescale.

Water softeners rely on a process called “cation exchange”, in which water passes through a resin tank that contains special resin beads. Those beads are heavily saturated with sodium ions. In some cases, potassium ions may be used as well.

As water passes through the resin tank, calcium and magnesium ions from the water are swapped out for the sodium or potassium ions. Once water exits the softener unit, it contains significantly fewer calcium and magnesium ions compared to the input water.

Water softeners need to be regenerated regularly to continue working optimally. This involves running a salt brine through the resin tank, which draws out all the hardness ions that have been captured by the resin during its operation.

salt-based water softener

Ion Exchange Filters

Ion exchange filters are essentially a variant of the approach we just described. The main difference between a water softener and an ion exchange filter, however, is that a water softener uses salt for the ion exchange process. This means that it must be regularly regenerated. An ion exchange filter uses a hydrogen cation exchanger to remove calcium and magnesium – the idea is the same.

Nanofiltration (NF)

Nanofiltration is a process that often gets confused with reverse osmosis. Both of them rely on similar principles, with the main difference being the size of the pores on the nanofilter. The membrane of a nanofilter typically has pores of around 0.001 microns in size – which, while still very small, is one order of magnitude larger than the pores on a reverse osmosis membrane. As a result, nanofiltration effectively removes various contaminants like calcium and magnesium, but it falls short in certain other areas, such as chloride. Still, this makes it great at reducing the hardness of water.

Does Brita Remove Limescale?

Brita filters are good at improving the overall taste and odor of your drinking water, but they’re far from thorough in terms of filtration capabilities. When it comes to limescale specifically, a Brita filter may remove large flakes of limescale, but that’s about it. If water hardness is your primary concern, you will need to look into an alternative mode of treatment.

Is Limescale in Drinking Water Harmful?

Limescale is not harmful for your health. It may add a certain unpleasant taste to your water, but it won’t do anything to your body. Appliances are a different story. Limescale buildups are one of the main factors that lead to the premature failure of washing machines and dishwashers. Limescale also tends to build up inside water kettles and coffee machines, making its way into the water treated by those appliances.


Coffee is one of the few things that are positively affected by limescale. Some coffee enthusiasts seem to prefer to prepare their brews with hard water, as certain levels of hardness actually improve the taste. This is very subjective though – others claim that limescale makes their coffee too bitter to be enjoyable. It’s also worth remembering that while you may enjoy the taste of hard water in your coffee, your coffee maker will not be very happy about it in the long run for the reasons we outlined above.

If you have any thoughts about the question, does reverse osmosis remove limescale, 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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