Is Reverse Osmosis Water Hard or Soft? Let’s Find Out!
Written by: Gene Fitzgerald // Last Updated: Apr 7, 2023
This page may contain affiliate links. If you buy a product or service through such a link we earn a commission at no extra cost to you. Learn more.
If you’re familiar with reverse osmosis, you’re likely aware that it’s one of the most thorough purification methods for water available right now.
And yet, despite its popularity, reverse osmosis still seems to attract some misconceptions. For example, some people aren’t even sure if reverse osmosis water is harder or softer than regular water.
Here are some things you should know about that.
Contents
show
Key Takeaways
- Reverse osmosis water is soft.
Is Reverse Osmosis Water Hard or Soft?
Is reverse osmosis water hard or soft?
Reverse osmosis water is soft. That’s because the filtration process removes various impurities which contribute to water hardness: Primarily calcium and magnesium carbonates. While reverse osmosis doesn’t remove all impurities at 100% efficiency, it still reduces their concentration to levels low enough that they can be considered negligible.
This means that in some cases you might even be able to use a reverse osmosis system without needing a water softener at all. This, however, depends on the kinds of minerals you have in your water supply, as well as your overall goals.
What Is Hard Water? What Is Soft Water?
Some people associate the terms hard water and soft water with factors like taste. In reality, the hardness of water is primarily defined by the concentration of certain elements. Calcium carbonate is the main element here. Its concentration in the water is what determines its hardness, primarily.
Here is an overview of the current guidelines for determining water hardness based on the concentration of calcium carbonate:
- 0 – 60 mg/L is soft water
- 61 – 120 mg/L is moderately hard water
- 121 – 180 mg/L is hard water
- 180+ mg/L is very hard water
How Soft Is Reverse Osmosis Water?
The main factor which determines how soft your reverse osmosis purified water will be is the hardness of your input water. Reverse osmosis gets rid of more than 95% of total dissolved solids (TDS), including calcium carbonate. This means that the higher the concentration of dissolved solids in your input water is, the harder your output water will be – and vice versa!
For example, if you’re filtering water with 500 mg/L hardness, meaning very hard water, you will be left with roughly 25 mg/L in the filtered water which categorizes as soft. With hardness of 150 mg/L for the input, you will get just 7.5 ppm in the filtered water.
Why Is Reverse Osmosis Water Soft?
As we described above, the main reason behind the softness of reverse osmosis water is the fact that the process removes various elements which contribute to its hardness, mainly calcium carbonate.
In general, reverse osmosis removes many contaminants and impurities with a high level of effectiveness. In fact, it’s one of the most effective filtration methods available for drinking water on the market right now. This means that reverse osmosis also gets rid of various other solids which may contribute to the hardness of your water.
What’s the Difference Between Reverse Osmosis and Water Softening?
Even though reverse osmosis softens water as a natural effect of its operation, that’s not the intended effect of the process. Reverse osmosis was originally designed to get rid of harmful and aesthetic water contaminants as effectively as possible. This includes stuff such as lead, chromium 6, and cadmium; calcium carbonate not so much.
How does reverse osmosis work? It uses a semipermeable membrane with very fine pores. These pores allow water molecules to diffuse through them while rejecting almost everything else. Any contaminants remain on the feed water side of the RO membrane and are flushed down the drain in the wastewater stream.
On the other hand and as the name implies, water softening was specifically designed to make hard water soft. This is done by treating it with sodium in an ion exchange process. Essentially, hard water enters a water softener and gets in contact with a bed of tiny resin beads. This beads are supercharged with sodium. As the hard water gets in touch with the beads and sodium, the hardness minerals in the water replace the sodium sticking to the resin. The sodium goes into solution. All accumulated hard water minerals remain in the softening tank until they are flushed out during a regular regeneration cycle which also recharges the softening resin with salt.
Bottom line: Reverse osmosis and water softening have a completely different purposes, they work entirely different, and thus achieve different outcomes.
By the way, the two processes are not mutually exclusive. In fact, they can benefit each other in certain regards. You should read on if you’re dealing with water that is particularly hard but also heavily contaminated.
Further Reading:
Which Is Better?
It’s hard to say which of the two processes is better. This depends on your individual needs and situation. If your primary concern is dealing with hard water, then you might be able to just use a water softener without a reverse osmosis system. However, if you face real water contamination, you definitely want to look into reverse osmosis.
The point is, each of those processes has a specific application. In this regard, it doesn’t make sense to describe either one as inherently better.
Can You Use Both?
Yes, it’s perfectly possible to use a reverse osmosis water filtration system and a water softener in combination. In fact, doing that is recommended if you both hard water + contamination.
Typically you would run your water through a softener first, and after that filter it through a reverse osmosis system. That way your reverse osmosis filter will get rid of almost all sodium that was introduced into the water by the softener.
This may not matter much to you in some cases, but it’s important to consider in certain situations. For example, if you’re using soft water for gardening, you should know that sodium can have a harmful effect on some plants. This means that filtering your water with reverse osmosis before using it for such purposes is going to be an improvement. You might also have issues related to sodium in your diet. Many people naturally consume a lot of sodium from their food. Removing excess sodium from your water can be great for your health.
Feeding your reverse osmosis system with soft water will also have the benefit of a much longer membrane life. You see, RO membranes are very delicate and prone to clogging. Clogging can be caused by introducing hard water to an RO system. But if you use a water softener for pre-treatment, there will be no hard water to begin with.
Combining a reverse osmosis system with a water softener allows you to enjoy the best of both worlds. You won’t have to worry about the hardness of your water nor about any harmful contamination.
If you have any thoughts about the question, is RO water soft water, please don’t hesitate to leave a comment below!
About the Author Gene Fitzgerald
Information provided on BOS is for educational purposes only. The products and services we review may not be right for your individual circumstances.
We adhere to strict editorial guidelines. Rest assured, the opinions expressed have not been provided, reviewed, or otherwise endorsed by our partners – they are unbiased, independent, and the author’s alone. Our licensed experts fact-check all content for accuracy. It is accurate as of the date posted and to the best of our knowledge.