What are raw water, softened water, desalinated water, pure water, and ultrapure water?

Raw water refers to untreated water. Generally speaking, the water before entering the water treatment process is also referred to as the raw water of the water treatment process. For example, the water sent from the water source to the clarification tank for treatment is called raw water.

Softened water refers to water in which the hardness (mainly calcium and magnesium ions) is removed or reduced to a certain extent. During the softening process of water, only the hardness decreases while the total salt content remains unchanged

Desalinated water refers to water in which salts (mainly strong electrolytes dissolved in water) are removed or reduced to a certain extent. Its conductivity is generally 1.0-10.0 μ s/cm, resistivity (25 ℃) 0.1-1000000 Ω. cm, and salt content is 1.5mg/L.

Pure water refers to strong and weak electrolytes (such as SiO2, CO2, etc.) in water. Remove or reduce water to a certain extent. Its conductivity is generally 1.0-0.1 μ s/cm, and its resistivity is 1.0-1000000 Ω· cm. Salt content<1mg/L.

Ultra pure water refers to water in which the conductive medium is almost completely removed, while gases, colloids, and organic substances (including bacteria) that do not dissociate are also removed to a very low degree. Its conductivity is generally 0.1-0.055 μ s/cm, resistivity (25 ℃)>10 × 1000000 Ω. cm, and salt content<0.1mg/L. The ideal pure water has a theoretical conductivity of 0.05 μ s/cm and a resistivity of 18.3 × 1000000 μ s/cm at 25 ℃.

Desalinated water refers to the finished water obtained by using various water treatment processes to remove suspended solids, colloids, inorganic cations, anions, and other water impurities. Desalinated water does not mean that all salts in the water have been completely removed. Due to technical reasons and considerations of water production costs, desalinated water is allowed to contain trace impurities according to different uses. The less impurities in desalinated water, the higher the water purity.

The hardness of water is mainly composed of cations such as calcium (Ca2+) and magnesium (Mg2+) ions. When raw water containing hardness passes through the resin layer of the exchanger, calcium and magnesium ions in the water are adsorbed by the resin, while sodium ions are released. The water flowing out of the exchanger is softened water with hardness ions removed. When the resin adsorbs calcium and magnesium ions to a certain saturation, the hardness of the effluent increases. At this time, the water softener will automatically regenerate the failed resin according to the predetermined program, using a higher concentration of sodium chloride solution (salt water) to pass through the resin and restore the failed resin to a sodium type resin.

Desalted water refers to the finished water obtained by using various water treatment processes to remove suspended solids, colloids, inorganic cations, anions, and other water impurities. Desalinated water does not mean that all salts in the water have been completely removed. Due to technical reasons and considerations of water production costs, desalinated water is allowed to contain trace impurities according to different uses. The less impurities in desalinated water, the higher the water purity. In production practice, people use different names to distinguish the purity of desalinated water based on the concept of desalinated water. For example, in boiler feedwater treatment, water with conductivity less than 3uS/cm (25 ℃) is usually referred to as distilled water, water with conductivity less than 5us/cm (25 ℃) and SiO2 content less than 100ug/L is referred to as primary desalinated water, water with conductivity less than 0.2us/cm (25 ℃) and SiO2 content less than 20ug/L is referred to as secondary desalinated water, and water with conductivity less than 0.2us/cm (25 ℃), Cu, Fe, Na content less than 3ug/L, and SiO2 content less than 3ug/L is referred to as high-purity water or ultrapure water. Salt content in water is the reason for water conductivity. The higher the salt content of water, the lower its resistance, and the stronger its conductivity. In other words, the strength of water's conductivity is an inevitable reflection of its salt content. The conductivity of water can be easily measured using a conductivity meter. The conductivity of water can be used to measure its purity. Because water temperature has a significant impact on conductivity, generally for every 1 ℃ increase in water temperature, conductivity increases by about 2%. Therefore, conductivity should indicate water temperature. The conductivity of various ions varies, so water with the same conductivity may have different types and contents of impurities. The conductivity generated solely by the ionization of H and OH - in water at 25 ℃ is 0.555 us/cm, which is the theoretical limit for the purity of desalinated water. Conductivity and resistivity are reciprocal to each other, i.e. conductivity=1/resistivity, for example, 0.2us/cm=5M Ω· cm. The above definition and water quality standards for desalinated water are not yet fully unified, especially with significant differences between different industries. For example, some industries refer to water with conductivity less than O.lF6/cm (25 ℃), pH value of 6.8-7.0, and removal of other impurities and bacteria as high-purity water. In there. In some industries, desalinated water is also known as pure water, desalinated water, saltwater free water, and purified water.

Working principle of softened water: The hardness of water is mainly composed of cations such as calcium (Ca2+) and magnesium (Mg2+) ions. When raw water containing hardness passes through the resin layer of the exchanger, calcium and magnesium ions in the water are adsorbed by the resin, while sodium ions are released. The water flowing out of the exchanger is softened water with hardness ions removed. When the resin adsorbs calcium and magnesium ions to a certain saturation, the hardness of the effluent increases. At this time, the water softener will automatically regenerate the failed resin according to the predetermined program, using a higher concentration of sodium chloride solution (salt water) to pass through the resin and restore the failed resin to a sodium type resin. Soft water reduces or avoids the formation of scale, making it suitable for washing and bathing. In addition, it also avoids energy waste and reduced efficiency of water equipment caused by scale in water pipes. The main characteristics of soft water are: 1. Preventing water pipes, water heaters, coffee machines, humidifiers, steam irons, bathtubs, shower heads, flush toilets and other household appliances from accumulating scale, frequently clogging, and low thermal efficiency. 2. Hairdressing, dandruff removal and itching relief, gentle hair, natural hairstyle. Skincare, bathing, soft and smooth skin, significantly reducing body dandruff. Makeup, the skin does not feel tight, making it easy to apply makeup and remove makeup. 3. Brewing coffee and brewing tea leaves, with a unique taste and pure flavor. Nurture flowers, extend flowering period, leave no spots on green leaves, and have vibrant flowers. Fish farming to prevent various fish diseases. 4. Extend the shelf life of tofu, make soybean milk more fragrant, and do not need auxin for bean sprouts. Wash vegetables, remove pesticide components, and extend the shelf life of vegetables. Cooking rice shortens the time, the rice grains are soft and smooth, and the noodles are not easily swollen. Cooking to maintain the natural taste and nutritional content of vegetables. 5. Effectively inhibit fungi, promote wound healing, and reduce the incidence of constipation, gastrointestinal and stone related diseases. 6. Laundry, prevent static electricity, discoloration, and deformation, clean tableware, keep it clean and free of water stains, and improve the glossiness of utensils. Clean the kitchen and bathroom, effectively remove dirt and odors. 7. Save expenses by reducing water equipment and pipeline maintenance costs by over 60%, hot water fuel costs by over 30%, and detergent purchase costs by over 50%. The applicable fields of softened water include bathrooms, kitchens, laundry, heating, boilers, central air conditioning equipment water supply, beauty and health care, and many other fields.

Information source: New Perspectives on Water Treatment