Do water filters reduce the hardness of tap water? Water softener vs water filter

Do water filters reduce the hardness of water? – Aquaseep

Water softeners and water filters are two of the compulsory household products we see each day. The first one is necessary for reducing the hardness of the tap water. The second one gives us clean and fresh drinking water.

But, can we use water filters in place of a water softener to soften water? The answer is we can, and only reverse osmosis water filters can do the trick. 

But, will there be any consequences? In this post, we’ll be discussing how RO water filters can give us soft water and why you shouldn’t follow it permanently.

Now, let’s go and find out more about soft and hard water.

What is hard water?

When tap water contains an excessive amount of Calcium and Magnesium ions, we refer to it as hard water. The feed water we get each day comes with a variety of minerals.

According to a study, nearly 85 percent of the municipalities serve the citizens’ hard water with plenty of minerals. In a residential setting, the hard water will do more harm than good.

  • When you apply soap into hard water, the Ca2+ and Mg2+ ions react with soap molecules. Due to the reaction, the soap turns into insoluble compounds. As a result, you will see scum gathering on the surface of the water.

Foams won’t form, and the soap loses its ability to wash. Furthermore, the ions from the hard water will dampen the color of your clothes. 

In addition to these, hard water also causes limescale to build up inside the pipes and tubes. A continuous flow of hard water inside the water heater can significantly reduce its lifetime and efficiency by building up a Calcium deposit around the heat exchanger.

Can water filters reduce the hardness of water?

Reverse osmosis water filters can significantly reduce the hardness of the water. Meanwhile, Carbon block water filters can’t get rid of the Calcium and Magnesium ions.

Therefore, you can see, not all types of water filters are effective when it comes to softening the water. The sediment filters remove dust, rust, clay, debris, and other undissolved molecules.

On the contrary, the Carbon block filters see out Chlorine, Chloramine, Arsenic, VOCs, odor, and other organic contaminants. But, the sediment filters and carbon block filters cannot filter out the dissolved molecules from the water.

As the Calcium and Magnesium ions remain as ions or dissolved solids in the water, the sediment or carbon block water filters cannot reduce the hardness.

  • Meanwhile, the reverse osmosis water filters come with a RO membrane. During filtration, it gets rid of 95% of dissolved solids from the water. Consequently, the Ca2+ and Mg2+ ions also get filtered in the process.

But, if you have an alkaline RO filter, the water hardness problem won’t get solved. In this type of filter, there remains a post-filter that restores the minerals into the water. And, doing so replenishes the hardness as well.

So, you see, only a pure RO water filter without any post-alkaline filter can soften the water. The sediment, Carbon block, or alkaline filters aren’t effective at all.

How do RO water filters convert hard water into soft water?

The RO water filters come with a reverse osmosis membrane that only lets water molecules pass through. Thus, any other substance other than water gets filtered out. And, as the Calcium and Magnesium ions get flushed out, the water becomes softer. 

In general, all RO water filters possess a sediment filter and a carbon block filter. These two work to eliminate dust, rust, and organic compounds from the water.

All that is left is the water molecules and the dissolved chemical compounds among them. Now, the water enters the RO chamber and encounters the RO membrane, or reverse osmosis membrane.

  • Due to the selectivity property of the membrane, the water flow breaks into two different flows. The first one contains only the water molecules, devoid of dissolved solids. We call this one the permeate water.
  • On the other hand, the left out minerals combine with a portion of water and create RO-reject water. We also know this as wastewater. About 3 gallons of water go to waste for producing a single gallon of purified water.

So, you see, the permeate water doesn’t contain any form of dissolved solids. As a result, you wouldn’t find Calcium or Magnesium ions in it. And, through this process, the RO filters produce soft water out of the tap water containing plenty of minerals.

If you would like to know further about how reverse osmosis works, check out our post here. You can also see another post where we discuss why water gets wasted during reverse osmosis. Click here to check out the post.

Are Reverse osmosis water filters more efficient in creating soft water?

When it comes to efficiency, water softener stays miles ahead of any reverse osmosis water filter. But, when it comes to purification, there is no alternative for water filters.

The water softeners stand out in two different aspects.

  • Firstly, the water softeners can treat bulk volumes of water at a time. The reason is water softeners rely on an ion-exchange procedure. The ion exchange takes place all around the resin bed. As a result, much of the water gets treated as it enters the softener tank. 

Meanwhile, the water has to pass through a membrane inside a RO water purifier. As the filter doesn’t have a tank before the RO membrane, it can only treat a meager amount of water at a time.

  • Secondly, water softeners don’t waste as much water as water purifiers. On average, 3 gallons of water go to the drain to give you one gallon of pure water.

On the other hand, only 25-30 gallons of water get used in the regeneration process inside a water softener. On this note, you need to discharge your water softener after every 3000 gallons of water it treats.

Therefore, the wastewater to product water ratio in a water softener is nearly 120:1. The ratio stands at 3:1 inside a RO water purifier.

So, you see, water softeners are way more efficient than RO water filters in producing soft water.

Should I use a water filter instead of a water softener to soften water?

There is no alternative to a water softener when it comes to softening water. Although RO purifiers can get rid of Calcium and Magnesium ions, those fall short on the aspect of efficiency.

But, in case you don’t have a softener installed at home or your softener is damaged, you might use a RO water filter momentarily. 

But, regular usage of a RO water purifier will cause permanent damage to the RO membrane. As a result, you will need to replace the filter cartridges much more often. On top of that, as the reverse osmosis process takes time in a residential setting, your daily chores will have to wait.

So, you see, using a RO water filter instead of a water softener can’t be the permanent solution. Only in case of emergency, you might employ a water purifier to get soft water. And replace it with a water softener as soon as possible.

If you would like to know how often you should change the filter cartridges, you should check out our post here.


Throughout this post, we tried to explore how RO water filters can reduce the hardness of the water. We also showed you why you shouldn’t employ this regularly.

Water softeners are specialized for only producing soft water. Therefore, those will trump over RO water filters in the job any day. But, in case of emergency, you can employ a water purifier without an alkaline filter attached.

So, have you found your answers? Or, do you still have some questions left? Let us know in the comments. And if you want to see more posts like this, you can check out our blog page here. Cheers!!!

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