Reverse Osmosis vs. Alkaline vs. Ionized Water

If you have been comparing water treatment systems, you’ve likely run into three terms that often get lumped together: reverse osmosis, alkaline, and ionized water. While they may be marketed as alternatives to each other, they are not. One is a purification technology, while the other two are pH treatments. Confusing them can lead to getting a system that doesn’t address your real water concern. 

This guide compares reverse osmosis vs. alkaline water vs. ionized water and breaks down how each works, the impurities they remove, their cost, and which is a better choice for your home.

Reverse osmosis (RO) water has a pH around 5.5 to 6.6 (after air exposure) and is purified by pushing water through a semi-permeable membrane that removes 95% to 99% of dissolved contaminants. Alkaline water has a pH of 8 to 9, and is produced by adding magnesium and calcium to water through a mineral cartridge. The water tastes better but isn’t cleansed of contaminants unless passed through a filter. Ionized water is made through electrolysis. It has a pH of 8.5 to 9.5 and a mineral charge, but it isn’t purified of fluoride or any other impurities like RO water. 

Key Takeaways:

• Reverse osmosis purifies water of up to 99% contaminants, including heavy metals, microplastics, PFAS, fluoride, nitrates, and bacteria, making it completely safe and healthy for consumption. RO water, however, tastes flat to some people.

• Alkaline and ionized systems mainly adjust the water’s pH, but they don’t remove contaminants besides some chlorine, tastes and odors.

• RO with remineralization is the best fit for households that want comprehensively treated but great-tasting water.

• Of the three systems, ionizers provide you with the most flexibility over your water’s pH but have the highest upfront cost, and can only work on water that contains minerals. 

• Alkaline filters raise the water’s TDS count because they dissolve minerals into water, but a higher TDS reading doesn’t always point to water contamination.

• Test your water before buying any system so you can get one that best complements your needs and fixes the quality concerns in your water.

Quick Answer: Which One Should You Choose?

Reverse osmosis removes 95% to 99% of dissolved contaminants, including microplastics, lead, arsenic, nitrates, hardness minerals, chlorine, volatile organic compounds (VOCs), bacteria, microplastics, forever chemicals, bacteria, and viruses, making it the perfect solution when your water quality report shows any of these. 

Alkaline filters primarily raise the water’s pH by adding minerals, so alkaline water is better-tasting, but it isn't purified of contaminants unless you add a filtration layer to it. Ionizers use electrolysis to adjust the water’s pH and require minerals in the source water, but they don’t remove the dissolved salts. 

For most Canadian households, RO combined with remineralization works well, delivering ultra-pure water with a balanced taste.

RO vs. Alkaline vs. Ionized Water Side-by-Side Comparison

The comparison table below provides a quick snapshot of the differences between alkaline, reverse osmosis, and ionized water.

What Is Reverse Osmosis Water?

Reverse osmosis is a water purification process that pushes water against its natural osmotic pressure to pass through a semi-permeable membrane with pores as small as 0.0001 microns. This process removes up to 99% of dissolved contaminants, including lead, arsenic, nitrates, fluoride, per- and polyfluoroalkyl substances (PFAS), also known as forever chemicals, bacteria, viruses, chlorine, and hardness minerals. The resulting water is called ‘reverse osmosis water.’

Calcium and magnesium are naturally present in tap water and buffer its pH. But when RO removes them along with different contaminants, the water becomes slightly acidic. Fresh RO water is close to neutral (around pH 7), but the pH drops to approximately 5.5 to 6.5 when it absorbs carbon dioxide to form weak carbonic acid on getting air exposure. 

Yes, RO water is acidic, but this pH shift is not a health concern at all. The World Health Organization (WHO), Health Canada, and U.S. Environmental Protection Agency (EPA) do not set a minimum guideline for drinking water’s pH and don’t consider RO water’s slightly low pH a safety issue.

What Is Alkaline Water?

Alkaline water is water that has a pH of around 8.5 to 9.0, which is higher than that of regular tap water, which is around pH 7.0. The higher pH is due to dissolved calcium and magnesium in the water.

Water can be naturally alkaline if it passes through mineral-rich bedrock before reaching your tap. Tap water can be made alkaline using the following three measures:

• Mineral cartridges: These include inline filters and pitchers and are the simplest of the lot as they don’t require any electricity and produce no wastewater. They raise the water’s pH by about 1 to 2 points, depending on the source water’s pH.

• Water ionizers: They use electrolysis to break down water molecules, splitting them into alkaline and acidic water streams. Alkaline water is sent to the tap while the acidic stream is used for cleaning. The alkaline water’s pH is between 8.5 and 9.5.

• Bottled water or alkaline drops. Most bottled water is alkaline. You can also get alkaline drops to raise the water’s pH.

Alkaline treatment dissolves minerals into the water, so the overall total dissolved solids (TDS) count increases, which answers a common query: does an alkaline filter increase TDS? 

A TDS meter is unable to distinguish contaminants from minerals, so if your TDS count shows high, it is likely not a sign of contamination, particularly if you combine alkaline treatment with water purification. If you don’t, getting a professional water test is a wise move.

What Is Ionized Water?

Ionized water is made through electrolysis, a process that uses an electric current to separate water into two separate streams: acidic and basic (alkaline). A semi-permeable membrane and two charged electrodes are used in the process.

The water molecules split at the electrodes, with the alkaline stream rich in calcium and magnesium collecting at the cathode (negative electrode) and the acidic stream saturated in sulfate and chloride ions collecting at the anode (positive electrode). Both the streams flow simultaneously; the alkaline stream is sent to the drinking water tap, while the acidic stream is moved to the other taps where water is used for cleaning purposes.

All ionized drinking water is alkaline, but not all alkaline water is ionized. Mineral drops and cartridges also raise the pH without using electricity. Ionizers can only function if the source water contains minerals. If you use an RO system to purify water, remineralize it if you wish to ionize it.

Manufacturers and marketers claim ionized water acts as an antioxidant, as it can have negative Oxidation-Reduction Potential (ORP) values of -600 to -850 mV. However, a research study published in the National Library of Medicine shows that any potential antioxidant influence and therapeutic effects of ionized water are due to dissolved molecular hydrogen (H₂), not ORP itself.

Here’s the most important part: ionizers don’t treat water the way RO does. They do use ultrafiltration and carbon, which only removes chlorine and some visible particles, but don’t tackle salts, nitrates, fluoride, lead, and other hazardous contaminants.

How to Choose Between Reverse Osmosis, Alkaline, and Ionized Water

Deciding between alkaline water vs. reverse osmosis, or RO vs. ionized water? The decision comes down to your taste preference, water profile, health requirements, and budget.

Choose RO If Your Water Report Shows Contaminants

If your private well test or municipal water quality report shows the presence of arsenic, nitrate, mercury, lead, chromium-6, high TDS, or microplastics, a reverse osmosis system is the most reliable solution. It is also suitable for homes with high sodium and fluoride concerns in water, pregnant women, infants, and those with compromised immune systems. 

RO removes the widest range of dissolved contaminants while keeping your costs low in the long run.

Choose an Alkaline Filter If Your Water Is Already Safe

If your tap water is clean with no contaminant concerns in the municipal report or independent water assessment, and you want your drinking water to be mineral-rich and taste refreshing, go for an alkaline water. It is excellent for renters or those who don’t wish to modify their existing plumbing. Plus, it doesn’t produce any wastewater, unlike RO.

However, if your water has safety concerns, it is better to invest in a comprehensive water treatment system like reverse osmosis. For a balanced taste, you can add an alkaline remineralization stage to it. Some alkaline pitchers do come with a carbon block that removes chlorine and unwanted odors and taste, but it doesn’t purify like RO. 

Choose a Water Ionizer If You Want Adjustable pH

Want more control over your water’s pH? A water ionizer lets you do that with the push of a button. Depending on your preference, you can change it from mild to strongly alkaline. No other water treatment system provides this level of flexibility and freedom.

However, ionizers are a big investment. Among reverse osmosis, alkaline, and RO + alkaline units, they carry the highest upfront cost. Their filtration ability is also limited to ultrafiltration and carbon, so they don’t address dissolved salts and contaminants like RO does.

And while manufacturers make bold claims about ORP and hydrogen, there is limited supporting evidence. So opt for an ionizer only to get control over your water’s pH and taste, not for unproven health claims.

Choose RO With Remineralization If You Want Purity and Minerals

RO with remineralization is a combo that delivers the best of both worlds: you get RO-level water purification plus minerals added back to your water, which improves its taste. The resulting water’s pH is between 7.5 and 8.0, which fixes the flat taste people dislike in plain reverse osmosis water.

If you want a complete solution that tackles your water’s contaminants and taste, choose an RO system with an additional remineralization stage.

Can You Combine Reverse Osmosis and Alkaline Water?

Yes, you can combine reverse osmosis and alkaline water to get ultra-pure water that is both cleansed of up to 99% harmful contaminants and has a crisp and delicious taste. 

Here are two ways to get that result.

RO With a Remineralization Cartridge

The semi-permeable RO membrane eliminates up to 99% of impurities, with the remineralization cartridge adding back the calcium, potassium, and magnesium that were previously removed by the membrane. The water’s pH spikes to 7.5 to 8.0 from 6.5. Calcium carbonate cartridges increase the pH by 1 to 2 points without making the water hard, which can cause limescale formation. This is the simplest way to get pure, great-tasting water from one system.

You can either get an RO system with an additional remineralization stage or buy a separate remineralization cartridge and integrate it into your system. Just make sure you choose a cartridge that is compatible with your existing filter.

RO with a Remineralizer and a Water Ionizer

You can also combine an RO system with a remineralizer and water ionizer. Reverse osmosis kicks out all the dissolved contaminants, followed by the remineralizer rejuvenating the water with magnesium and calcium, and finally the ionizer raises the pH via electrolysis.

To use an ionizer with reverse osmosis, you need to add a remineralizer in between the two stages because ionizers can only function in the presence of minerals.

Well, this setup is comprehensive and gives you amazing water quality, it is quite expensive and requires you to address the maintenance requirements of three different systems. And the installation is quite complex too.

The Real Cost: 5-Year Cost of Ownership

The table below provides a quick overview of the 5-year cost of ownership of each of the four systems.

The cost of wastewater varies by municipal rate. Considering the typical Canadian rate of $3 to $4 per cubic meter, an inefficient RO system using 3 gallons per gallon produced adds roughly $30 to $60 every year for a family of four. High-efficiency systems can significantly reduce this cost. 

Note: Prices vary by brand and region.

Health Claims: What's Proven and What Isn't

Among the different health claims surrounding alkaline and ionized water, most lack strong scientific backing. The ‘Nutrients In Drinking Water’ report by WHO raises concerns regarding low-mineral water and how it affects our health when we drink water with very few minerals in it, particularly when the level drops below 100 mg/L TDS. That said, what’s important to understand is that food is still the primary source of nutrients, including minerals for most people. 

As for the pH concerns, Health Canada treats slightly acidic low-mineral water as safe. pH adjustment is primarily related to taste. Remineralization takes care of this aspect for anyone seeking mineral-rich water.

Our kidneys and lungs regulate our blood pH tightly between 7.35 and 7.45, irrespective of what you consume. There is limited research surrounding alkaline water’s health benefits. Few studies suggest some positive effects for post-exercise hydration and reflux. However, a more thorough review, including that by Mayo Clinic did not discover any differences between regular and mineral water.

As for ionized water, there has yet to be extensive research on how hydrogen supports our health.

3 Common Mistakes When Buying RO or Alkaline Water Systems

Steer clear of the following 3 mistakes when buying an alkaline or RO water system to ensure you get the right fit for your home.

• Buying alkaline to fix contaminated water: Alkaline filters are incapable of removing contaminants, such as lead, PFAS, or nitrates from water. Always test your water first then buy a system that matches the problem.

• Buying RO without planning for taste: Plain RO water tastes quite flat. If taste is your priority, budget for an RO system with a remineralization stage or a separate cartridge. 

• Skipping filter changes: A system works best when it is properly maintained. RO pre-filters demand replacement every 6 to 12 months. And the membranes ought to be changed every 2 to 3 years. Keep up with the routine and your system will always deliver refreshing and safe drinking water.

Checklist Before Buying an RO or Alkaline Water System

Don’t forget to check the following when buying an RO or alkaline water system.

• Test your water first: We cannot stress this enough. The journey to getting a water system, be it any, begins with testing your water. Get your municipal water quality report, and if it feels insufficient, get a professional water assessment.

• Check NSF/ANSI certifications, independent third-party standards that verify a filter's performance claims. Certification 42 is for taste and odor reduction, 53 stands for health-related contaminants like lead and cysts, 58 is specifically for reverse osmosis systems, and 401 is for emerging contaminants like PFAS and pharmaceuticals.

• Factor in local water rates, rental status, cabinet space, and your maintenance habits to pick a system that aligns with all these factors.

• If the water’s taste is really important to you, decide on remineralization upfront to save yourself time, hassle, and money later.

FAQs About Reverse Osmosis and Alkaline Water

Is reverse osmosis water better than alkaline water?

RO and alkaline water serve different purposes. RO water is filtered of up to 99% dissolved contaminants but is bland tasting, while alkaline water is better tasting but not cleansed of impurities. If you want safe and clean drinking water, choose RO. If you prefer a refreshing and balanced taste, choose alkaline water.

Is RO water acidic, and is that harmful?

Freshly treated RO water has pH 7. But when it is exposed to air, it absorbs CO₂, which forms weak carbonic acid. As a result, the water’s pH drops to 5.5 to 6.5. It is slightly acidic but completely safe to consume, according to Health Canada and the U.S. EPA.

Does reverse osmosis remove minerals from water?

Yes, RO removes most dissolved minerals from water, which includes calcium and magnesium. 

Can you make RO water alkaline?

Yes, you can make RO water alkaline by either adding an alkaline filter or remineralization cartridge to the system after the RO membrane or using alkaline drops to raise the drinking water’s pH.

Does an alkaline filter remove contaminants?

To a very limited extent. Some alkaline pitchers include carbon that removes chlorine, but they are ineffective for eliminating dissolved contaminants such as PFAS, fluoride, lead, or nitrates like RO does.

Why does my alkaline filter increase TDS?

Alkaline media dissolves minerals into water which raises the overall level of total dissolved solids. A TDS meter cannot differentiate between minerals and contaminants, so a higher reading doesn’t indicate contamination.

Is ionized water the same as alkaline water?

All ionized water is alkaline because it contains extra minerals and has a pH between 8.5 and 9.5. But all alkaline water isn’t ionized as ionized water is made through electrolysis, but alkaline water can be made using mineral drops and/or cartridges.

Does a water ionizer work with RO water?

Not directly. Plain RO water doesn’t contain minerals, and ionizers can only work with minerals present in water. To use an ionizer with an RO system, you need to introduce a remineralization stage or alkaline filter in between the two stages. The remineralization cartridge adds back minerals to water, and then the ionizer can ionize it.

Which is healthier: RO, alkaline, or ionized water?

For contaminant removal, RO is most protective. For mineral content and pH, alkaline or remineralized RO water offers benefits. Health claims around ionized water have limited evidence. Match the system to your water quality first.

Choosing the Right Drinking Water for Your Home

Deciding among RO, alkaline, and ionized water for your home comes down to understanding your household needs, preferences, water quality concerns, and budget. 

RO is a filtration technology. It works best when there are existing contaminant concerns or potential risks in your water. If your water is otherwise safe, but you are unhappy with its taste, choose an alkaline filter. But if you want more control over your water’s pH and can afford an ionizer, opt for it. For most homeowners, RO with remineralization stage works best.

And if you have decided to invest in an RO system but cannot find a quality system, check out illi water’s brilliant range of advanced reverse osmosis systems designed specifically for Canadian water conditions.