Does Reverse Osmosis Soften Water Reducing Its Hardness?

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Are you trying to choose between a water softener and a reverse osmosis system to treat your hard water? There are definitely some things you need to consider.

A lot depends on the quality of water you have coming into your home and whether or not it’s better to have both systems installed or just one.

While reverse osmosis technically softens water, is it really the best option to deal with your hard water? Let’s see.

Key Takeaways

  • Reverse osmosis does soften water.
  • However, it is not recommended to be used for that purpose as it will cause premature fouling of the reverse osmosis membrane.

Does Reverse Osmosis Soften Water and Reduce Hardness?

So, does reverse osmosis soften water?

Yes, reverse osmosis does soften water and reduce its hardness. However, that is not what reverse osmosis was designed for, and it shouldn’t be used as a water softener for hard water on its own, as too much calcium and magnesium can build up on the RO membrane causing it to decrease in effectiveness.

If you are working with hard water, installing a water softener at the point of entry of your feed water is ideal to soften it before it reaches your RO system.

Is Reverse Osmosis Water Hard or Soft?

Water hardness is caused by too many minerals in water, specifically calcium and magnesium. As reverse osmosis is excellent at filtering these minerals out of the water, then the water coming from the reverse osmosis system is soft by default.

blue reverse osmosis membrane

If Reverse Osmosis Removes Hard Water, Do I Still Need a Water Softener?

It depends on the condition of your water. If you do have hard water, a water softener is the “treatment method, as it protects all the pipes and fixtures in your home from limescale and residue buildup. A water softener will also eliminate spotting on glassware and staining on bathroom fixtures, etc.

No reverse osmosis system can do that, unless it’s a whole house model which is considerably more expensive.

And even if you have a whole house reverse osmosis system, if you are running it with hard water, then you will wear out your reverse osmosis membrane quickly. Once the membrane is clogged from the buildup, it won’t filter as effectively, and it will filter much slower.

So, in short, yes, you still need a water softener if you have hard water.

The Effects of Hard Water on an RO Membrane

Water hardness causes scaling of the reverse osmosis membrane, which damages its ability to filter contaminants from your water. This reduces both the water quality and pressure and may increase the amount of wastewater produced.

Then there are cost factors. Needing to change the RO membrane all the time or needing to backwash the system constantly can be costly and inconvenient.

It is often essential to have your water tested when you are considering a reverse osmosis system to see if it is necessary to have a water softener installed and check with the manufacturer about the maximum TDS level that your RO filter system can handle (usually it is around 2000 ppm)

Reverse Osmosis Systems vs Water Softeners – Differences and Which to Choose

With the exception of ‘they both soften water’, the two types of systems are entirely different and designed for different purposes.

  • Water softeners were designed to soften water, and RO systems were designed to filter contaminants from water.
  • A water softener is usually installed where the water supply enters the home, softening all the household water, whereas RO systems are mostly point-of-use.
  • Water softeners use ion exchange to replace calcium and magnesium ions with soft sodium ions. It conditions the water, whereas RO purifies the water rejecting impurities.

So, which should you choose? Well, if you have issues with hard water in your home and not any problems with the quality of your drinking water, then a water softener. If you need to remove contaminants from your water, and your water is not hard, a reverse osmosis system is the better choice. If you have both hard water and contaminants you want to remove from your drinking water, then you will likely need both.

How Reverse Osmosis Works

A reverse osmosis water filtration system usually comprises 3 to 5 filter stages, including a sediment pre-filter, activated carbon pre and post-filters, the reverse osmosis stage itself, and sometimes post-filtration steps such as a remineralization filter.

These steps ensure that the reverse osmosis system removes most of the harmful contaminants from drinking water, while keeping the delicate membrane in optimum condition.

Reverse osmosis itself is the term used to describe the filtering of water through a semipermeable membrane that has tiny pores. These pores are so small that while they allow small molecules such as H2O through, larger molecules are trapped on the other side and disposed of down the wastewater drain.

When in good working order, a reverse osmosis system can filter out:

  • Metals including lead, cadmium, chromium, nickel, and mercury
  • VOCs (volatile organic compounds)
  • Microbes like bacteria, cysts, and protozoa
  • Water disinfectants (chlorine and chloramine)
  • Disinfection byproducts
  • Pesticides and herbicides
  • Minerals and salts
  • Sediment and silt
  • Nitrogen
  • Overall total dissolved solids (TDS)

How Water Softening Works

Traditional water softening works by removing calcium and magnesium ions from the water with a salt-based water softener.

The purpose of a softening unit is primarily to prevent the build-up of limescale in your plumbing system and household appliances to protect them from premature wear out. Plus, there are the aesthetic benefits.

salt-based water softener

Water softeners are most commonly installed at the household water’s point of entry so that they soften the water in the entire home.

They are simple systems, usually containing a resin tank with a bed of microbeads covered in sodium or potassium ions. The hard water enters the line and is sent to the softener, through the resin tank, and then to the distribution tube. As it does this, it is exposed to resin beads that exchange ions to soften the water.

After a few days, most of the resin beads will be coated with hard minerals and unable to soften. Then the resin will recharge using salt stored in a brine tank.

What Are the Benefits of Using Reverse Osmosis AND a Water Softener?

If you have hard water, and want to purchase a reverse osmosis system, not only is installing an additional softener beneficial, it may actually be necessary. Again, have your water tested to assess its level of TDS.

A Softener Will Protect an RO Unit

An RO unit can be a costly investment, and you want to ensure it lasts a long time! A water softener will act as a layer of extra protection for your RO system, by reducing the hard minerals it is exposed to that may lead to the unit under-functioning or requiring more frequent maintenance or replacement.

High-Quality Water

Using both systems together ensures that your water is of the highest purity. Not only will a water softener protect your household pipes and make laundry cleaner, and showering better for your skin, but adding a reverse osmosis system to the mix provides your household clean and safe drinking water from your kitchen sink.

Save Time And Money

While both systems require a certain amount of upfront investment, over time, it may save you money. RO systems mean no more buying bottled water and water softeners mean less detergent still goes a long way. Not to mention it increases the lifespan of your plumbing and appliances.

Health Benefits

RO water is free of contaminants that may harm your health, and softened water is better overall for your hair and skin.

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