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Distilled water

physical science Maturity 9-11 Next article →

Distilled water is a highly purified form of water. It is created through a process called distillation. This method removes impurities from water or other fluids. These impurities are often non-volatile components. Non-volatile means they do not boil at the same temperature as water.

Double Distilled Water Unit
Double Distilled Water Unit

Common impurities include minerals like calcium, magnesium, sodium, fluoride, potassium, iron, and zinc. By boiling the water, these substances stay behind in the original container. This prevents the buildup of mineral deposits, often called scale. Scale can damage machines like boilers or steam engines.

The mechanism of distillation follows a specific sequence of steps. First, the source water is heated until it reaches its boiling point. This heat turns the liquid water into vapor, or steam. The steam then rises and moves into a separate container. In this second container, the vapor is cooled down. This cooling causes the vapor to condense back into a liquid state. Because the minerals did not turn into vapor, they remain in the first container. The resulting liquid in the second container is the purified distilled water.

Steam water distiller
Steam water distiller

Distillation technology has changed significantly throughout history. Ancient writers like Aristotle mentioned the distillation of water in the *Meteorologica*. Around AD 200, Alexander of Aphrodisias provided a clear description of the process. Later, in 1797, Captain Israel Williams recorded an improvised method in his journal. Before World War II, distilling seawater was very expensive. It often required one gallon of fuel to produce just one gallon of fresh water. Dr. R. V. Kleinschmidt changed this by developing the Kleinschmidt still. This device used steam compression to make the process much more efficient. During World War II, these stills became standard equipment on Allied ships.

Aqua-distillata
Aqua-distillata

Modern science allows for very precise measurements of distilled water. Commercial equipment can reduce the Total Dissolved Solids (TDS) to less than 1 part per million (PPM). This process also lowers electrical conductivity to less than 2 μS/cm. In contrast, typical tap water has much higher conductivity, ranging from 200 to 800 μS/cm. The pH of distilled water is also unique. It is always slightly lower than the neutral value of 7. This happens because the water absorbs carbon dioxide from the air. This absorption forms traces of carbonic acid, lowering the pH to around 5.8.

There are many practical applications for this pure water. In industrial settings, distilled water is used in steam irons. This prevents limescale buildup and helps the iron last longer. It is also vital for medical equipment like CPAP machines. These machines use distilled water to humidify air for breathing without leaving contaminants behind. Even early aviation used this technology. The Boeing 707 used distilled water to increase air density for jet engines during takeoff.

Steam water distiller
Steam water distiller

However, using distilled water for drinking is a complex topic. It has not been proven to be healthier than hard water. Hard water contains minerals like magnesium and calcium. These minerals can help protect against nutritional deficiencies. Some studies suggest that drinking hard water is linked to beneficial cardiovascular effects. For example, hard water consumption is negatively correlated with atherosclerotic heart disease. For optimal health, magnesium levels should be between 20 and 30 mg/L. Calcium levels are often recommended between 40 and 80 mg/L. Because distilled water lacks these ions, people must get them through their diet.

Distillation is part of a broader field of water treatment. While distillation is very effective, other methods exist. For instance, reverse osmosis and deionization are common alternatives. In laboratories, scientists sometimes use "double distilled water" for extreme purity. In biological studies, researchers must be careful with distilled water. Adding it to an aquarium might actually remove necessary minerals. Living things in lakes or oceans have evolved to need specific mineral ranges. Therefore, understanding the chemistry of water is essential for both technology and biology.

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File:Aqua-distillata.jpg
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File:Double Distilled Water Unit.jpg
Double Distilled Water Unit.jpg
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Steam water distiller.JPG
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