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The Effects of Hard Water on RO Filter Systems

Hard water is water with high mineral content, the most common minerals being calcium and magnesium.

While these minerals are beneficial for our health, they can cause serious problems when it comes to reverse osmosis water treatment. What these problems are and what negative side effects they have on RO filter systems, we are going to discuss in the following post.

Effects of Hard Water on Reverse Osmosis Membranes

One of the most notable effects hard water has on reverse osmosis systems is membrane scaling. As the semipermeable membrane is the heart of every RO system, scaling can result in a total system shutdown.

The following is a list of the most problems and their effects as a result of membrane scaling due to overly hard feed water.

If you want to learn more about how to troubleshoot a malfunctioning RO system, click here.

1. Reduced Water Quality

Scaling directly leads to membrane aging. An aged membrane is porous and less effective at removing impurities. Undesired substances may leak into your otherwise clean water.

Even though some systems use 2 consecutive membranes to ensure that all contaminants are filtered out, the filtration performance of these membranes is threatened the moment they get in touch with hard water.

The overall effect is a decrease in water quality and it can’t be guaranteed that the filtered water is still safe for direct consumption.

2. Higher Costs

As is expected with any filter system, regular maintenance is key to ensure that your RO unit works as intended and remains functional for as long as possible.


However, if your system has to process exceptionally hard water, even the best model requires more maintenance than usual.

In other words, maintenance checks have to be conducted more frequently, which leads to additional costs you will have to cover, for example for more frequent membrane replacements.

3. Increased Water Wastage

Increased water wastage is yet another serious problem posed by hard water that you’ll have to deal with. It occurs because pressure drops behind the membrane once the water has passed through it. As a result, all subsequent filtration stages can’t perform as efficiently as they normally would.

To achieve the same level of purity, your RO system has to flush more wastewater down the drain. This is not only bad for the environment as water is a very precious resource and  its scarcity is becoming a bigger issue year after year. You also have to pay a higher water bill.

Damage to the Entire System

The negative effects hard water has on RO systems are not limited to membranes alone.

And indeed, if water hardness isn’t properly monitored, your entire system is bound to break in the near future. Because as scaling escalates, water pressure in front of the membrane will continue to grow. This pressure is likely to damage other system parts and eventually cause leakages.

Caution Sign

BOS Bonus Tip: Even if hard water is not an issue in your home, we always recommend our customers to turn off the feed water supply to their filtration system when they are not at home.

The simple reason for that being that you can never be 100% certain that no leakages will occur while you are away. Leaking water can damage wooden floors, carpets and walls among other parts of the building.

Measures of Prevention

In order to guard yourself against reduced water quality and higher costs due to constant membrane replacements and higher system maintenance, regular monitoring of the quality of your feed water is key. This is the only way to ensure that scaling does not become a serious issue.

If you detect excessive amounts of hardness minerals in your water, you have multiple options for treatment.

Usually, minerals responsible for hardness have to be identified as a first step, as not all of them can be removed in the same manner. If, for instance, hardness is caused by too many iron ions, you have to apply a specialized iron filter. For hardness caused by calcium, a regular softening system should do the trick.

Once you know what you are dealing with, everything becomes much easier. Simply install the right treatment system and you are good to go.

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