Basic Knowledge About Water (Classified)

The molecular formula of water is H₂O, with a relative molecular weight of 18.015. Hydrogen makes up 11.9% of the water molecule, and oxygen makes up 88.81%.

Water salinity: also known as mineralization, it indicates the amount of salts in the water, or the sum of the amounts of various anions and cations.

Hardness: The total concentration of metal ions in water after cations combine with anions to form scale.

Conductivity and resistance: The purer the water and the lower its salt content, the higher its resistivity and the lower its conductivity. Ultrapure water conducts almost nothing. Conductivity is equal to the reciprocal of resistance.

pH value and acidity/alkalinity: The pH value of water is the negative logarithm of the hydrogen ion concentration, also known as the hydrogen ion index. It indicates whether the aqueous solution is alkaline, neutral, or acidic.

High-quality water: High-quality drinking water obtained through further processing of municipal water supply (or standard water) using processes such as coarse filtration, fine filtration, ultrafiltration, and sterilization.

Mineral Water: A precious water resource from nature, supplied to consumers as commercial drinking water after simple sterilization and filtration.

Purified Water: Clean water with virtually no impurities, obtained using water treatment equipment with a high desalination rate. Its conductivity is generally 1.0~0.1 μS/cm.

Mineralized Water: Pure mineralized water containing trace elements, obtained by adding mineral rocks to relatively pure raw water using a special process.

Softened Water: Water whose hardness (mainly calcium and magnesium ions) has been removed or reduced to a certain extent. During the softening process, only the hardness decreases, while the total salt content remains unchanged.

Desalinated Water: Water in which salts (mainly strong electrolytes dissolved in water) have been removed or reduced to a certain extent.

Pure Water: Water in which strong and weak electrolytes (such as SiO2 and CO2) have been removed or reduced to a certain level. Its conductivity is generally 1.0-0.1 μS/cm, resistivity (25℃) 0.1-1.0*106 Ω·cm, and salt content <1 mg/L.

Ultrapure Water: Water in which electrolytes are almost completely removed, and non-decomposable gases, colloids, and organic matter (including bacteria) are also removed to very low levels. Its conductivity is generally 0.1-0.55 μS/cm, resistivity (25℃) 10.0*106 Ω·cm, and salt content <0.1 mg/L. Ideal pure water (theoretically) has a conductivity of 0.05 μS/cm and a resistivity (25℃) of 18.3 × 10⁶ Ω·cm.

Groundwater: This is water formed by rainwater seeping through soil and strata. During its long journey and extensive contact, it dissolves a significant amount of salt, resulting in extremely high hardness. However, groundwater undergoes multiple filtration processes, leaving very little suspended solids, resulting in clear water with low turbidity.

Surface water: This refers to rainwater, snowmelt, river water, lake water, and ocean water. Except for ocean water, which has extremely high salt content, other surface water is characterized by low salt content and low hardness, but it often contains high levels of pollutants. Municipal water supply (tap water) mainly refers to municipal water that has been treated at water treatment plants. This is a common form of drinking water. Due to the significant differences in source water across different areas, national standards are relatively lenient. After sedimentation, filtration, and chlorination disinfection at water treatment plants, the water is delivered to households. This method produces relatively stable water quality, with minimal fluctuations. However, the water undergoes only minimal processing and has a wide range of uses. It's impossible to separate industrial, domestic, and drinking water, making it unsuitable for meeting the high standards and requirements of drinking water for the general population. Furthermore, the secondary pollution caused during the long transportation or storage process is severe. People are forced to boil the water before use, but while boiling kills bacteria, it fails to remove other impurities. In fact, some substances become more concentrated with boiling, posing a health risk.