Demineralized water, demi & osmosis: the difference

What is demineralized water?

Demineralized water is water from which dissolved minerals, salts, and ions have been removed. Think of calcium, magnesium, sodium, chloride, and other substances normally found in tap water. What remains is almost pure water with very low conductivity and virtually no limescale.

The term is often abbreviated to "demi" water. The two terms mean exactly the same thing: "demi" simply stands for demineralized. You often encounter the term in connection with irons, car batteries, boilers, and laboratories, because low-mineral water does not cause limescale or malfunctions there.

There are two main ways to make it. With ion exchange, water flows through resin beads that exchange mineral ions for hydrogen and hydroxide ions. With reverse osmosis, water is forced under pressure through a membrane that blocks up to 99% of dissolved substances. Both produce low-mineral water, with a small difference in purity.

Demineralized, demi, osmosis or distilled water: what is the difference?

The terms are easily confused, while the difference lies mainly in the production method and the degree of purity. Below, we list them for you.

Demineralized water and demi water

These are two names for the same product. Demineralized water is made by removing ions from the water, usually via an ion exchanger. The minerals are replaced by hydrogen and hydroxide ions, which together form water again. The result is low-mineral water that you often find in stores as demi water.

Osmosis water

Osmosis water is created by reverse osmosis. The water is forced under pressure through a semi-permeable membrane that blocks approximately 95 to 99% of dissolved substances. Technically, osmosis water is also low-mineral, but it still contains a small residue of ions. In practice, people therefore often call osmosis water a form of demineralized water.

Distilled water

Distilled water is made by boiling water and catching and condensing the vapor. Salts, minerals, and most impurities are left behind. Distilling takes a lot of energy because the water must first be brought to a boil, which makes it more expensive than demineralized water created via ion exchange or osmosis.

What do you use demineralized water for?

Because demineralized water contains almost no limescale or salts, it is ideal for applications where minerals actually cause problems. The most important applications are:

• Irons and steam systems: no limescale that clogs the steam holes, which makes the appliance last longer.
• Car batteries and cooling systems: low-mineral water prevents deposits and conducts less, which prevents malfunctions.
• Boilers and central heating systems: filling with demi water limits limescale formation in pipes and the boiler.
• Aquariums and plants: enthusiasts use osmosis water to accurately set water values.
• Washing windows and cars: without minerals, the water dries spot-free, without limescale streaks.
• Laboratories and industry: for measurements and processes that require absolutely pure water.

At PureAqua, we see that customers who make osmosis water at home often use it for multiple purposes at once: pure drinking water at the tap and low-mineral water for the iron or plants. One system, multiple applications. Also check out all the jobs for which osmosis water is suitable.

Benefits of demineralized water

Low-mineral water has a number of clear advantages, especially regarding limescale, purity, and the longevity of your appliances:

• No limescale: without calcium and magnesium, no limestone is formed in appliances and pipes.
• Longer lifespan of appliances: irons, coffee machines, and boilers last measurably longer.
• Very pure: via reverse osmosis, up to 99% of dissolved substances are removed, including PFAS, microplastics, drug residues, and pesticides.
• Neutral taste and odor: without dissolved salts, the water has no limescale or chlorine taste.
• Versatile: one source covers ironing, washing cars, aquariums, and, with a mineral filter, drinking water too.

Important considerations: can you drink demineralized water?

Pure demineralized or distilled water is not toxic, but it is not ideal to drink as a regular water source. The reason is simple: it lacks the minerals that your body absorbs through water.

According to the World Health Organization (WHO), drinking water contributes to the daily intake of calcium and magnesium. Water with almost zero minerals does not provide that contribution and can also taste a bit bland. For incidental use, a sip is no problem, but as a regular drinking water source, low-mineral water is less suitable.

That is why a good reverse osmosis system works with an extra step. It first filters the water until it is almost pure, after which a mineral filter adds calcium and magnesium back in. This way, you get water that is pure but still retains a natural taste and essential minerals. At PureAqua, The Source does exactly that, completely without electricity. We list what else is involved with this technique in the considerations of osmosis filtration.

Comparison table: the water types side by side

Buying advice: which pure water is right for you?

If you only occasionally want low-mineral water for your iron or battery, a bottle of demi water from the store is sufficient. If you use it more often or also want pure drinking water, making osmosis water yourself is often cheaper and more sustainable than buying bottles every time. Also check out where you can get osmosis water and what it costs per liter.

If you are looking for a plug-and-play solution without installation, the Countertop RO is a handy choice: you put it on the kitchen counter and draw osmosis water directly. You can read exactly how such a device works in our explanation about osmosis on the counter without a plumber. If you would rather have an invisible system in the kitchen cabinet with a stylish pure water tap, then The Source is the tidier solution. Both provide low-mineral water that you make drinkable with a mineral filter.

Frequently asked questions

Conclusion

Demineralized water and demi water are the same: low-mineral water that does not deposit limescale and is ideal for appliances. Osmosis water is a closely related variant that arises via reverse osmosis, and distilled water is generally the purest but the most expensive.

If you also want to drink this water, a mineral filter is the key: it adds back calcium and magnesium for a natural taste. With a system like The Source from PureAqua, you can create pure osmosis water yourself right at the tap, which removes up to 99% of unwanted substances and works without electricity. Over 950 customers have already preceded you, with a rating of 9 or higher.