Why Water Can Dissolve So Many Things—and How We Make It Safe to Drink

Water is called a universal solvent because it can dissolve more substances than any other liquid. This special property makes water very important in nature and in our daily lives. In chemistry, when a substance dissolves in water, the substance being dissolved is called the solute, the water is the solvent, and the mixture formed is called a solution. For example, when sugar is mixed into water, sugar is the solute, water is the solvent, and the sweet liquid you get is the solution. Similarly, if you stir salt into water, the salt disappears and forms a salt solution. Many substances like salt, sugar, and some gases dissolve easily in water, which is why water is so useful for cooking, cleaning, and even in our bodies. However, not everything dissolves in water—oil, for example, does not mix with water, showing that 'universal' does not mean water can dissolve every single thing.

A saturated solution is one in which no more solute can dissolve at a given temperature; any extra solute will remain undissolved. An unsaturated solution is one that can still dissolve more solute. When you keep adding sugar to a glass of water and stirring, there comes a point where no more sugar dissolves—this is a saturated solution. If you add only a little sugar and it all dissolves, the solution is unsaturated. Stirring helps solute particles mix faster with the solvent, so the solute dissolves more quickly. Increasing the temperature also helps more solute dissolve, because the particles move faster and mix better. For example, sugar dissolves much faster and in larger amounts in hot tea than in cold water. A common mistake is to think that stirring or heating can make an unlimited amount of solute dissolve, but even with stirring and heating, there is always a limit to how much can dissolve at a given temperature.

Water that is safe and fit for drinking is called potable water. Potable water should be clear, colourless, odourless, and free from harmful germs and chemicals. River water is not potable as it contains dirt, germs, and other impurities. To make river water safe for drinking, it goes through several steps: (1) Sedimentation with loading—heavy impurities settle at the bottom, and potash alum is added to help fine particles settle; (2) Filtration—water passes through layers of sand and gravel to remove smaller particles; (3) Aeration—water is exposed to air to remove bad odours and add oxygen; (4) Chlorination—a small amount of chlorine is added to kill harmful germs; (5) Storage—the treated water is stored in clean tanks. At home, water can be made safe by boiling (which kills germs) or distillation (which removes both germs and dissolved impurities). For example, many people boil water during the monsoon to prevent diseases. Some think clear water is always safe, but it may still contain invisible germs or chemicals.

Water pollution is mainly caused by adding harmful substances to water bodies. The main causes are domestic sewage (wastewater from homes), industrial effluents (waste from factories), and pesticides (chemicals used in farming). Polluted water can spread diseases such as cholera and typhoid. To conserve water, we can use methods like rainwater harvesting, where rainwater is collected and stored for use. Other ways include fixing leaking taps, using water wisely, and reusing water where possible. For example, water used to wash vegetables can be used to water plants. Some people believe that water is unlimited, but in reality, clean water is precious and needs to be conserved for everyone’s benefit.