Ultrapure Water System Water Quality Basics—water Quality Indicators

The application of ultrapure water systems is inseparable from water quality. Both the influent and output water of an ultrapure water system require strict quality assessment. In using our ultrapure water systems, we see many data indicators, most of which point to water quality; therefore, water quality is the soul of an ultrapure water system. So what are the water quality indicators? Let's take a look today:

1. TDS Value

TDS refers to the total dissolved solids (TDS) content in water. It is commonly used to measure the quality of source water, and the measuring tool is a TDS meter. The measurement principle is actually to indirectly reflect the TDS value by measuring the conductivity of water. The more dissolved solids in water, the higher its TDS value and the higher the conductivity of the water. Typically, TDS is about half the conductivity test value. In China, the TDS value of tap water in cities along the Yangtze River is usually 100–200 ppm, while in the Yellow River basin it is usually 300–600 ppm.

Note: TDS value and water salinity (also known as mineralization) are two different concepts. TDS value is usually greater than water salinity because TDS includes not only dissolved salts but also dissolved organic matter. 1. **TDS (Total Dissolved Solids) Value:** Only when water is very clean and has a very low organic matter content can the TDS value be used to approximate the salinity (or mineralization) of water. Generally speaking, TDS value, mineralization, and salinity are directly proportional to the concentration of these three substances in water.

2. Turbidity: Turbidity occurs due to the presence of suspended and colloidal particles in water. The degree of turbidity is called turbidity (measured in degrees). One degree of turbidity is defined as 1 mg of SiO2 (silicon dioxide) in 1 liter of water. The national standard for drinking water requires a turbidity of less than 5 degrees.

3. Hardness: Water hardness refers to the content of dissolved calcium, magnesium, and other metallic salts in the water (calcium salts account for approximately 85%, magnesium salts 10-15%, and other metallic salts 1-3%). It mainly refers to the content of Ca2+ and Mg2+ ions in the water. The Ca2+/Mg2+ in water primarily originates from the dissolution of calcium and magnesium salts (CaCO3/MgCO3) from rocks. When the CO2 content in the water is high, the dissolution rate is greatly accelerated. Hardness is divided into temporary hardness (carbonate hardness, which can be removed by heating and precipitation) and permanent hardness (non-carbonate hardness, which cannot be removed by heating and boiling). The sum of both is called total hardness. Internationally, the unit of water hardness is the German hardness (DHD). One liter of water containing 10 mg of CaO (calcium oxide) is considered 1 DHD. Water with a hardness greater than 8 degrees (equivalent to 200 ppm) is considered hard water. China's national standard for drinking water stipulates that the total hardness should not exceed 450 ppm.

4. PH Value

pH value represents the negative logarithm of the H+ concentration in water, also known as the hydrogen ion index. pH value indicates the magnitude of the change in acidity or alkalinity of a solution.

Strongly acidic aqueous solution: pH < 5.0

Weakly acidic aqueous solution: pH = 5.0–6.4

Neutral aqueous solution: pH = 6.5–8.0

Weakly alkaline aqueous solution: pH = 8.1–10

Strongly alkaline aqueous solution: pH > 10