Water Classification in Ultrapure Water System Applications

Before using an ultrapure water system, a crucial step is understanding the quality of the incoming water source. Different water qualities require different purification solutions, making this a vital step in selecting the right ultrapure water system. In other words, understanding water classification is extremely important. So today, let's take a closer look at water classification:

1. Groundwater vs. Surface Water

Groundwater: Less contaminated with organic matter and microorganisms, but contains more dissolved calcium and magnesium ions, resulting in higher hardness and a tendency to form scale. Sometimes, iron, manganese, and fluoride ions exceed standards, failing to meet the needs of production and domestic water use.

Surface Water: More contaminated with organic matter and microorganisms than groundwater. If the area is limestone, its surface water often has high hardness, such as in Deyang, Mianyang, Guangyuan, and Aba in Sichuan Province.

2. Hard Water vs. Soft Water

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 considered hard water. Hard water has many disadvantages in use; it easily reacts with detergents to produce precipitates, and scale formation after heating significantly impacts boiler heat circulation systems and other production processes. It usually requires softening/desalination treatment.

Soft Water: Water with lower hardness compared to hard water.

3. Raw Water vs. Purified Water

Raw Water – This typically refers to the water entering 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. In China, the TDS value of municipal tap water is typically 100–400 ppm.

Purified Water – Water that has undergone treatment by water treatment facilities is called purified water.

4. Pure Water vs. Distilled Water

Pure Water – Raw water that has undergone treatment by reverse osmosis and sterilization devices, removing most inorganic salt ions, microorganisms, and organic impurities, making it safe for direct consumption.

Distilled Water – Pure water prepared by distillation, typically not used for drinking.

5. Pure Water and Ultrapure Water

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).

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 μS/cm (resistivity >10 MΩ·cm). Theoretically, the purest water has a resistivity of 18.24 MΩ·cm.

6. Purified Water and Water for Injection

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

Water for Injection – Purified water that has been further purified by multi-effect distillation/ultrafiltration to remove pyrogens before being used to prepare injectable solutions.