pH and Chemistry of Water
Water’s role as a universal solvent and how its acidity or basicity shapes chemistry, biology, and the environment.
Pure water has a neutral pH of 7 at 25°C. In reality, natural waters almost always contain dissolved substances that shift the pH higher or lower. Understanding this chemistry is essential for drinking water safety, aquatic life, agriculture, and industry.
What is pH?
pH measures the concentration of hydrogen ions (H⁺) in a solution. A pH below 7 is acidic; above 7 is basic (alkaline). Each whole number change represents a tenfold difference in acidity or alkalinity.
Water as a Universal Solvent
The polar nature of the water molecule allows it to dissolve a wide range of substances — salts, sugars, acids, bases, and many organic compounds. This property makes water the medium for almost all chemical reactions in living cells and in the environment.
Natural and Human Influences on pH
- Dissolved carbon dioxide forms weak carbonic acid, slightly lowering pH
- Limestone and other minerals can raise pH (buffering capacity)
- Acid rain from industrial emissions can lower the pH of lakes and rivers
- Agricultural runoff and industrial discharges can cause local pH changes
Why pH Matters
Most aquatic organisms thrive in a relatively narrow pH range (roughly 6.5–8.5). Outside this range, fish, insects, and plants can suffer. In drinking water, extreme pH can affect taste, pipe corrosion, and the effectiveness of disinfection. In soils, pH controls nutrient availability for crops.
The chemistry of water is quiet but powerful — it determines what can dissolve, what can live, and how ecosystems and human systems function.