Classification of Water

By Location: Water can be classified as atmospheric water, surface water, and groundwater. Only 0.3% of freshwater participates in the water cycle, and the amount available for human use is even less. If all water in the hydrosphere were evenly spread across Earth’s surface, the average depth would exceed 2,718 meters—yet utilizable freshwater amounts to just 8 centimeters.

By Natural Form: Seawater, glacial water, lake water (reservoir water), and deep groundwater. Currently, the utilization rates of seawater and deep groundwater are very low. Drinking water is primarily sourced from lakes and reservoirs.

By Quality Characteristics: Mineral water, mountain spring water, purified water, distilled water, tap water, and mineral-added water (which technically should be classified as a beverage).

By Calcium and Magnesium Ion Concentration (Hardness): Soft water and hard water. Hardness below 8 degrees is classified as soft water; above 8 degrees as hard water. One degree corresponds to 10 mg of calcium oxide per liter.

By pH Value: Acidic water, neutral water, and alkaline water. Neutral water is ideal for drinking. Weakly alkaline and weakly acidic waters are both considered within the neutral water range.