Evaporated water is very clean because the process of evaporation leaves impurities behind.
The Evaporation Process and Purity
When water evaporates, it changes from a liquid to a gas (water vapor). According to the provided reference, this process happens when the sun warms the water on the Earth's surface. During evaporation, only the water molecules become vapor. Salts, pollutants, and other impurities that were dissolved in the water do not evaporate along with the water.
Why Impurities are Left Behind
The reason impurities stay behind is due to their physical properties:
- Boiling Point: Impurities like salts have much higher boiling points than water. Therefore, they require significantly more energy to change into a gaseous state. At the temperatures at which water evaporates, these impurities remain in their original state (solid or liquid).
- Molecular Weight: Water molecules are relatively light. The heat energy readily converts them to a gaseous state. In contrast, many dissolved impurities are heavier, larger molecules or ions, making it difficult for them to become airborne.
- Lack of Volatility: Many pollutants are simply not volatile, meaning they do not readily evaporate at common temperatures.
The Result: Pure Water Vapor
Because the impurities are left behind, the resulting water vapor is significantly purer than the original water source. This clean water vapor then rises into the atmosphere and can eventually condense to form clean rain. This natural process is harnessed in water purification techniques like distillation.
Examples of Impurities Left Behind
Here are some examples of what stays behind during evaporation:
- Salts: Sodium chloride (table salt), magnesium sulfate (Epsom salt)
- Minerals: Calcium, iron
- Pollutants: Pesticides, heavy metals
- Microorganisms: Bacteria, viruses
Practical Applications
This natural purification process is the basis for several important applications:
- Distillation: Heating water to evaporate it, then collecting the condensed water vapor, is a standard method for producing very pure water in laboratories and industries.
- Desalination: Evaporation is used in some desalination plants to remove salt from seawater, producing fresh drinking water.
