What Does a Reverse Osmosis System Remove from Drinking Water?

 

 

 

 

 

 

 

 

Most homeowners who decide to filter their drinking water eventually face the same question: how much filtration do I actually need?

A refrigerator filter, a water-filter pitcher and a reverse osmosis system can all improve drinking water, but they do not provide the same type or level of treatment.

In this article, we will use the term Basic Filtration Systems to describe common refrigerator filters, water-filter pitchers and simple activated-carbon drinking-water filters. These systems can be useful, particularly for improving taste and reducing chlorine, but they work very differently from reverse osmosis.

Understanding that difference makes it much easier to choose the right treatment system for your family.

Basic Filtration: Simple and Useful

Most basic household drinking-water filters rely primarily on activated carbon.

Activated carbon is particularly useful for reducing chlorine and improving taste and odour. This is one reason water from a refrigerator dispenser or filter pitcher can taste noticeably better than water directly from the tap.

For many homeowners, this may be exactly what they need.

If the main concern is simply chlorine taste or smell, a good carbon filter may provide a noticeable improvement.

However, better-tasting water does not necessarily mean that most dissolved substances have been removed.

Calcium, magnesium, sodium, fluoride, nitrate and many other dissolved substances can remain in the water after basic carbon filtration.

Some more advanced filters can reduce additional substances, so the capabilities of a particular filter should always be checked against the manufacturer's specifications.

Reverse Osmosis Works Differently

Reverse osmosis — or RO — goes considerably further than basic carbon filtration.

Instead of relying only on activated carbon, an RO system uses water pressure and a semi-permeable membrane to separate water from many dissolved substances.

A typical residential RO system may include several treatment stages:

Sediment Filter → Carbon Filter → RO Membrane → Post-Carbon Filter → Optional Remineralization

Each stage performs a different job.

The sediment filter helps protect the system from particles. The carbon stage reduces chlorine, improves taste and odour, and helps protect the membrane.

The RO membrane then performs the main reduction of dissolved substances.

Finally, a post-carbon filter can further improve the taste of the treated water before it reaches the drinking faucet.

What Does the RO Membrane Actually Remove?

The RO membrane acts as a highly selective barrier.

Water pressure moves water across the membrane while a large portion of many dissolved substances is rejected and carried away in a separate concentrate stream.

This allows a high-quality RO system to substantially reduce Total Dissolved Solids — TDS as well as many individual dissolved substances.

Depending on the membrane and system design, reverse osmosis can substantially reduce substances such as:

• fluoride;

• sodium and other dissolved salts;

• calcium and magnesium;

• nitrate and nitrite;

• lead;

• copper;

• arsenic;

• chromium;

• and many other dissolved substances.

RO membranes can achieve very high rejection rates. For many dissolved substances, reductions can exceed 90%, while certain systems and substances can approach 99% under appropriate operating conditions.

This does not mean that every RO system removes exactly 99% of everything. Actual performance varies according to the membrane, incoming water chemistry, pressure, temperature and condition of the system.

When selecting a particular RO system, the manufacturer's specifications should therefore be checked for the substances that are important to you.

Basic Filtration and RO Are Solving Different Problems

This is perhaps the easiest way to understand the difference.

A refrigerator filter or filter pitcher may do an excellent job of reducing chlorine taste and making tap water more pleasant to drink.

But much of the original dissolved mineral content may still remain.

Reverse osmosis changes the composition of the water much more significantly.

Its carbon stages can address chlorine, taste and odour, while the RO membrane substantially reduces TDS, dissolved minerals, salts and many other dissolved substances.

So if your primary goal is:

better taste and less chlorine smell,

basic filtration may be enough.

If your goal is:

substantially reducing dissolved substances in the water you drink and cook with,

reverse osmosis provides a much more comprehensive treatment approach.

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Convenience Matters Too

The difference is not only about what the systems remove.

It is also about how practical they are for everyday family use.

A refrigerator filter is convenient when you want a glass or bottle of cold water. But try filling a large cooking pot through a refrigerator dispenser and its limitations quickly become obvious.

The flow is usually relatively slow, and the dispenser was primarily designed for glasses and bottles rather than supplying several litres of cooking water.

A water-filter pitcher has a different limitation.

For one or two people it may be perfectly adequate. For a larger family, however, it can mean repeatedly filling the pitcher, waiting for the water to pass through the filter, emptying it and starting the process again.

An under-sink reverse-osmosis system provides treated water directly from a dedicated drinking-water faucet.

Open the faucet and use the amount you need.

That makes RO practical not only for drinking water but also for:

• filling reusable water bottles;

• making coffee and tea;

• filling kettles;

• cooking soups and sauces;

• preparing food;

• making ice;

• and filling pots with treated water.

For a family that uses several litres of drinking and cooking water every day, having treated water available directly at the kitchen sink can be a significant advantage.

Can You See the Difference in the Water?

Sometimes.

Water containing higher concentrations of dissolved minerals can leave visible deposits after boiling or evaporation.

A familiar example is the white mineral scale that can appear inside a kettle.

Ice made from tap water can also sometimes appear cloudy or show deposits as it melts. However, the appearance of ice should not be used as a test of water safety or purity. Air trapped during freezing can also make ice cloudy.

The more useful point is that a basic carbon filter does not necessarily remove dissolved minerals simply because the water tastes better.

One simple way to compare the difference is to measure Total Dissolved Solids — TDS.

Water passing through an ordinary carbon refrigerator filter or pitcher may still have TDS relatively close to the original tap water because most dissolved minerals pass through the carbon.

After reverse osmosis, TDS is normally substantially lower because reducing dissolved substances is one of the principal functions of the RO membrane.

This can also mean considerably less mineral residue in kettles and other applications using RO-treated water.

What Happens to Calcium and Magnesium?

Because reverse osmosis substantially reduces dissolved solids, it also removes much of the calcium and magnesium from drinking water.

Calcium and magnesium are important nutrients, but for people eating a reasonably balanced diet, food normally provides a much greater contribution than drinking water.

Mineral content does, however, affect taste.

Very low-TDS RO water can taste different from ordinary tap or mineral water. Some people prefer its clean, neutral character, while others prefer drinking water with some mineral content.

This is where remineralization becomes useful.

RO With Remineralization

Some reverse-osmosis systems include an optional remineralization stage after the RO membrane.

The concept is relatively simple.

First, the RO membrane substantially reduces the original dissolved substances in the water.

Then a remineralization cartridge introduces a controlled amount of selected minerals back into the treated water.

Depending on the system, these may include calcium and magnesium compounds.

The primary purpose is usually to adjust the final taste and mineral profile of the drinking water.

This gives homeowners two common options.

Standard RO provides highly treated drinking water with substantially reduced dissolved-mineral content.

RO with remineralization provides RO-treated water followed by controlled mineral addition for people who prefer a different taste and mineral profile.

Neither approach is automatically right for everyone. It depends on the desired result.

RO Does Not Replace a Whole-Home Water Softener

Reverse osmosis substantially reduces calcium and magnesium in the water it treats, but a residential RO system is normally installed at the point of use, most commonly under the kitchen sink.

It therefore performs a different job from a whole-home water softener.

A water softener treats the large volume of water used throughout the house — showers, bathrooms, the water heater, washing machine and other fixtures.

An RO system treats a much smaller volume of water primarily intended for drinking and cooking.

For homes with hard water, the two systems can work together very effectively:

Water Softener → hardness control throughout the home

Reverse Osmosis → additional treatment of drinking and cooking water

Which Level of Filtration Do You Need?

The easiest way to answer this question is to start with what you actually want from your drinking water.

If the main concern is chlorine taste and odour, a Basic Filtration System may be perfectly adequate.

If you want substantially lower TDS, dissolved minerals and salts, reverse osmosis provides a much higher level of treatment.

If there is a particular substance you want to reduce — such as fluoride, nitrate or lead — check the specifications of the particular system to determine its expected reduction performance.

And if you want highly treated RO water while retaining some mineral character, an RO system with remineralization provides another option.

The Bottom Line

A refrigerator filter, water-filter pitcher and reverse-osmosis system can all be called “water filters,” but they are not doing the same job.

Basic activated-carbon filtration is a simple and useful way to improve taste and reduce chlorine.

Reverse osmosis goes considerably further. Its membrane substantially reduces TDS and many dissolved substances that ordinary carbon filtration generally leaves behind.

RO also provides another practical advantage for families: treated drinking and cooking water is available directly from a dedicated kitchen faucet whenever it is needed, rather than requiring repeated pitcher filtration or relying only on a refrigerator dispenser.

The most useful question is therefore not:

“Which filter has the most stages?”

It is:

“What do I actually want to remove from my drinking water, and how do I want to use that water every day?”

For basic taste and chlorine improvement, carbon filtration may be enough.

For a substantially greater reduction of dissolved substances and convenient everyday access to treated drinking and cooking water, reverse osmosis provides a much more comprehensive solution.

And for homeowners who prefer some mineral character in their drinking water, remineralization makes it possible to add selected minerals after RO treatment and adjust the final taste and mineral profile.