Deionized Water vs Distilled Water: What’s the Difference

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Distilled WaterYou can compare the deionized water vs distilled water, but to say that the distilled water is the same as deionized water is a mistake. The terms “distilled water” and “deionized water” are often misunderstood. In this article, you can find the explanation to understand the differences and similarities of these two different water cleaning technologies.

The distilled water

The oldest method for production of pure water is the thermal method or distillation – water evaporation from the surface and condensation. The basis of the process is the transfer of water in the vapour phase with its subsequent condensation. The main drawback of this method is the very high maintenance costs of the electricity needed to convert the water into the steam. In addition, in the process of steam formation along with water molecules other solutes can enter the steam according to their volatility. Evaporation is achieved in various ways: the vacuum above the water, heating, etc.

Let’s consider the distillation. What’s happening in the process of distillation? The water molecules have the boiling point of 100°C or 212° F. Other substances have different boiling points. The substance that boils at a lower temperature evaporates first. The boiling point of various impurities is higher, and, theoretically, they will begin to evaporate, when the water has already boiled out. The substance that boils at a lower temperature evaporates first. Due to this difference the water is separated.Water Distillation

As a result, theoretically after the distillation the absolutely pure water is obtained. Actually, organic substances, which have similar boiling point than that of water can slip in the distilled water. For example, if the water contains the oil drops they can be found also in the distillate. There are practically no salts in the distilled water, because the salt boils at a much higher temperature. To eliminate the problem of organic substances, the water distillers have pre- and post water filters.

The absolute advantage of the distilled water is the complete absence of harmful substances.

Reverse Osmosis water or RO water

Reverse OsmosisThe latest alternative to the thermal method for obtaining of distilled water is a two-stage reverse osmosis. The technology is based on the double passage of raw water through a semipermeable membrane under the pressure. As a result, water is split into two streams: the filtrate (purified water) and concentrate (a concentrated solution of impurities). The two-stage reverse osmosis system can significantly reduce operational costs and improve the quality of obtained water. The reverse osmosis water treatment technology is the most common used in households and in the industry for preparation of drinking water.

Deionized water or DI water

Deionized water is deeply demineralized, ultrapure water with the resistivity close to 18 megohm-cm. It is used in microelectronics, printed circuit boards, instrument manufacture, pharmacy, washing liquids, etc.
In order to obtain the high quality pure deionized water, a multi-stage water purification process can be used. After pre-cleaning, the water is supplied to the reverse osmosis membrane, and then the water is filtered through a special deionization medium, which removes the rest of the ions in the water. The purity of deionized water can exceed the purity of distilled water.

Similarities and differences: deionized water vs distilled water vs reverse osmosis water

-> Deionized water vs distilled water – DI water is as pure as the distilled water or even purer;
-> Reverse osmosis water vs distilled water – RO water is more saturated with salts and oxygen than the distilled water and DI water;
-> Reverse osmosis and deionization are a more cost-effective than the distillation.

Distillation is used mainly in laboratories and factories, where it is needed. Reverse osmosis is widely used in water treatment plants, both at home and for manufacture of various drinks, bottled water, etc.

Distillation, RO and deionization processes are intended to purify the water of the contaminants: mercury, lead, strontium, nitrates, phosphates, manganese, as well pesticides.

2 Responses to “Deionized Water vs Distilled Water: What’s the Difference”

  1. Dmitri says:

    I heard that RO water filtration may not filter out fluoride. Is this true? Also do you know where I can find a detailed list of what RO does filter out? Thank you for your time and thanks for the information on this website. I found it useful.

  2. Jerry Garwell says:

    Thank you for your question. Actually the reverse osmosis water filter systems do remove fluoride. The purity of water you get from RO water purification system is close to distilled water because RO removes up to 99,9 % of all minerals and contaminants. Just look at any of the RO system specification and you will find the list. For example:
    iSpring 75GPD 5-Stage Reverse Osmosis Water Filter System

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