Water Classification in Water Treatment – ​​Save This for Later!

Water comes in many forms. Whether it's the water we encounter in daily life or water used in professional treatment, water can be categorized into many types. Based on factors such as form, source, and the content of dissolved impurities, water types vary greatly. They can be broadly classified as follows:

I. Groundwater and Surface Water

① Groundwater: Water buried below the surface in various forms, such as well water and water in rock cavities. Its characteristics include low levels of organic matter and microbial contamination, high content of ionic substances, generally high hardness, and a tendency to form scale.

② Surface Water: Water above the surface, such as rainwater, river water, lake water, and sea water. Its characteristics include higher levels of organic matter and microbial contamination, and greater influence from the surface environment. For example, surface water in limestone areas also has high hardness.

II. Hard Water and Soft Water

① Hard Water: The total concentration of metal ions such as calcium and magnesium in water is called hardness. Water with a hardness greater than 200 ppm (8 in Germany) is generally called hard water. Hard water has several disadvantages in use. It easily reacts with detergents to produce precipitates, and scale formation after heating significantly impacts boiler/heat circulation systems. Softening/desalination treatment is usually required.

② Soft water: Water with less hardness compared to hard water.

II. Raw Water and Purified Water

① Raw water: Usually refers to the influent to water treatment equipment, such as commonly used municipal tap water (internationally known as drinking water), suburban groundwater, and surface water from the wild. Its quality is usually measured by TDS (Total Dissolved Solids) value. The TDS value of municipal tap water in China is typically 100-400 ppm.

② Purified water: Raw water that has undergone treatment by water treatment facilities is called purified water.

III. Pure water and Distilled water

① Pure water: Raw water that has undergone a complete water treatment process, including reverse osmosis and sterilization devices, to remove most inorganic salt ions, microorganisms, and organic impurities. It is pure water that can be consumed directly.

② Distilled water: Pure water prepared by distillation, usually not used for drinking. IV. Pure Water and Ultrapure Water

① Pure Water: Deionized water prepared by reverse osmosis, distillation, ion exchange, etc. Its TDS value is typically <5 ppm, and its conductivity is typically <10 μS/cm (resistivity >0.1 MΩ·cm).

② Ultrapure Water: Pure water with extremely low ion content obtained by further purifying and deionizing pure water through ion exchange, distillation, electro-desalination, etc. Its TDS value is unmeasurable, and its conductivity is typically <0.1 S/cm (resistivity >10 MΩ·cm). Theoretically, the resistivity of the purest water is 18.248 MΩ·cm.

V. Purified Water and Water for Injection

① Purified Water: Pure water used in the pharmaceutical industry is called purified water. Its conductivity is typically required to be <2 μS/cm.

② Water for Injection: Purified water is further purified by multi-effect distillation/ultrafiltration to remove pyrogens before being used to prepare injectable solutions.