You have a seemingly limitless number of choices when it comes to buying water at your favorite grocery or retail store. It can be difficult to know which kind of water is best to buy for which purpose. If you want to buy drinking water, you want something that is safe and good tasting. If you’re buying water to clean, cook or run through a device such as a humidifier or vaporizer, you want something that is clean and pure. Plus, of course, cost is always a factor.
Two of the most common types of bottled water are distilled water and purified water. To decide which is better for your needs, you need to know the differences between the two. To understand the differences, we first need to define and examine what is meant by “distilled” and “purified.”
What Is Distilled Water?
Distilled water is water that is forced to change states of matter to remove impurities (minerals and chemicals found in tap water, ground water or rain water). It is changed from water to gas, and then back to water. Scientifically speaking, this is accomplished by the processes of evaporation and condensation. Water is generally evaporated into a gas by applying heat to boil it. The gas is captured and then exposed to cool temperatures to trigger condensation. Once the water condenses, it is collected, and is now distilled water.
The Distillation Process
To get a better picture of how the distillation process is achieved, let’s look at how it could be accomplished in your kitchen:
The distilled water you buy at the store is created in essentially the same way, just using massive machines in an industrial setting. It is important to note that most of the impurities typically found in tap water have a lower boiling point than water, which is why evaporation eliminates so many of them. However, some have a higher boiling point than water, which is why the process of distillation is more effective than simply boiling water and letting it cool.
What Is Purified Water?
Purified water is water that undergoes filtration and other processes to remove chemical and mineral impurities. It is important to note that while all purified water is filtered, not all filtered water is purified.
Physical Filtration Through Charcoal, Ion Exchange, and Reverse Osmosis
The filtration process can generally be divided into one of two categories: physical filtration and chemical filtration. Physical filtration, as the name would suggest, involves simply passing the water through materials that act like a sieve, leaving impurities behind and straining the “clean water” through. In chemical filtration, the water passes through a material or membrane and in doing so, creates a chemical reaction, the by-product of which is the removal of impurities. There are a variety of physical and chemical filtration techniques (including combinations of the two methods), but we will focus here on three of the most popular: physical filtration through charcoal, ion exchange and reverse osmosis.
Charcoal is a softer form of carbon and is both materially solid and chemically porous, which makes it an ideal natural sieve for the physical filtration of water. Most commercially available water-pitcher based filters use charcoal as the mechanism for their filtration. As water passes through the charcoal, many mineral impurities cannot pass through it, and are filtered out of the water that makes it into the pitcher.
The ion exchange method of purifying water is a good example of a chemical filtration process. While the chemistry involved is quite complex, we can give a brief overview that demonstrates the broad mechanics of how chemical purification is achieved. In an ion exchange, a chemical reaction causes a “bad” element (impurity) to be replaced with a “good” element (pure water).
The most common example of an ion exchange system is in a water softener. Salt is used as a catalyst to spark the chemical reaction to trade “bad” elements for “good.” Impurities are removed and water is softened for the tap, showers and appliances throughout a household. It is worth noting that the salt never actually mixes with the water; it just factors into the chemical reaction caused by the water and equipment.
Reverse osmosis is also a physical filtration process. It sounds very complicated, but it can be explained fairly easily. Osmosis itself is the act of water moving through some sort of semi-permeable (meaning relatively solid, but with some porousness) membrane. Due to the scientific principle of osmosis, water naturally moves from a higher concentrated form (purer water) to a lower concentrated form. That’s why reverse osmosis is a purification technique. By adding some sort of physical pressure generator into the technique, water is forced to move in the reverse direction, from less concentrated to more concentrated, therefore resulting in water that is more pure of minerals and chemicals. Most sink-based water filtration systems in homes and businesses employ a type of reverse osmosis system.
Now that we’ve clearly defined the different techniques to produce distilled water vs. purified water, we can examine the advantages and disadvantages of each method.
As you might imagine, distillation on any scale takes longer and involves more equipment than filtration. As the saying goes, “time is money,” and therefore, distilled water tends to be more expensive than purified water.
Many companies sell home water filtration and purification system-usually a Reverse Osmosis system that can be installed under a kitchen sink. These companies are quick to correctly point out that these systems are generally quite affordable, as opposed to purchasing all the equipment required to distill water on a large scale.
While charcoal filtration pitchers are probably the most affordable purification system commercially available, they vary considerably in the amount of impurities they can fully remove. Even the best filters on the market cannot remove impurities at the level that reverse osmosis systems can. Additionally, as filters wear out, they need to be replaced or they no longer serve their function as effectively. Over time, if a filter is not replaced, it can actually make the water in its pitcher less clear.
Taste is by its very nature subjective, so it’s hard to definitively say that either distilled or purified water is better tasting. The bottled water you buy at a convenience store or from a vending machine is typically purified rather than distilled, which may lead some to assume purified water tastes better. This is not necessarily the case, however, as different brands use different purification processes. Also, while specific impurities have to be at very low levels for water to be considered purified, some companies may place small amounts of harmless additives to improve flavor, or remove additional chemicals such as chlorine to create a more palatable taste.
It’s interesting to note that many people think distilled water is not drinkable because it is commonly recommended for use in machines like irons, vaporizers, and humidifiers. The reason distilled water works so well with those devices is that the amount of clogging mineral buildup is reduced significantly when distilled water is used instead of tap water.
Distilled water can be used to safely fill and replace water in aquariums. It can also be beneficial to “top off” certain types of car batteries. Some people also extoll the virtues of using distilled water to make ice cubes, as they tend to be exceptionally clear.
You may be surprised to learn that neither distilled nor purified water is intrinsically better for you. Arguments can be made for either, but ultimately both have had a large amount of impurities removed. They are both considerably better for you than drinking directly out of a faucet or a stream.
You should now have a better understanding of the differences between distilled water and purified water. While they undergo very different processes, the end goal is the same: mineral and chemical impurities are removed to provide clean, pure water. Distilled water has many practical household uses for machines and appliances since distillation reduces the amount of minerals that build up around faucets or vents. Purified water may have more flavor and cost less. While no technique can provide completely pure water, either is safer, cleaner alternative to unfiltered water.