Tap water can be said to be a defecation project to change our lives. As long as the tap is turned on, the water can “splash” out, which is hygienic, safe and convenient. While enjoying the convenience, we can not help but have these questions: how is the tap water commonly used everyday come from? What procedures have been taken to “wash white” step by step and become safe drinking water? Sometimes we may find that the tap water at home is muddy and milky white, or there is scale after boiling. Is such tap water safe? < / P > < p > the source of tap water, i.e. water source, is usually rivers, lakes, groundwater and surface water. The choice of water source needs to be considered in many aspects, which not only requires good water quality, easy health protection, but also must meet the requirements of water quality standards. < p > < p > the raw water without treatment contains slight particles such as algae, humus and sediment. After the raw water is taken from the water source by the water intake pump station of the water plant, it is necessary to enter the water plant and experience “experience” before entering the thousands of households. < p > < p > coagulation is to add coagulant to the raw water, so that the suspended solids and colloidal particles that are difficult to settle naturally in the water will agglomerate with each other to form large flocs and precipitate in the sedimentation tank to become sludge for removal. Filtration is to use granular filter material to intercept the residual particles in the water after sedimentation, further remove the impurities in the water and reduce the turbidity of the water. Coagulation, sedimentation and filtration can reduce the turbidity of water, at the same time, it can also remove bacteria and viruses. In order to meet the quality requirements of drinking water, it is necessary to disinfect and inactivate pathogenic microorganisms in drinking water. The commonly used disinfectants are chlorine, chloramine, chlorine dioxide, etc. < / P > < p > it should be noted that in some areas, due to the inherent deficiency of water quality, the operation of water treatment is more complex, and the water treatment system of water treatment plant has higher requirements. On the other hand, in order to improve the quality of effluent, the water plant is also gradually improving the traditional conventional treatment process. < / P > < p > in water treatment, some water plants will carry out biological pretreatment before the conventional treatment process, and remove ammonia nitrogen, organic pollutants, odor, iron, manganese, etc. through the metabolism of microorganisms, so as to achieve the purpose of purifying water quality and reduce the burden of subsequent conventional process water treatment. The activated carbon is also used as advanced treatment technology in the water plant. Activated carbon is colorless and tasteless, has a large specific surface area and a large number of micropores, so it can effectively adsorb non-polar compounds in water. Among them, granular activated carbon (GAC) is not easy to be lost, renewable and reused, which is often used in continuous operation of water treatment process, while powdered activated carbon (PAC) is cheap and does not need to add special equipment and structures, especially suitable for water purification treatment of seasonal water quality and sudden accidents. At the same time, due to the short reaction time and low dosage of ozone pre oxidation, the pretreatment process of raw water using ozone has gradually begun to be widely used. Ozone has strong oxidation, which can directly oxidize and produce oxidized hydroxyl radicals. It can oxidize and decompose many organic pollutants in water. Moreover, ozone has strong bactericidal, decolorizing, algae removing and coagulating AIDS. In addition, membrane water treatment technology, a new technology developed in recent years, has been gradually applied to waterworks. Membrane water treatment technology uses the pressure difference between the two ends of the membrane as the power to treat pollutants. According to the size of pollutants and pressure, it can be divided into nanofiltration (NF), microfiltration (MF), ultrafiltration (UF) and reverse osmosis (RO) nanofiltration membranes. Different membrane pore sizes are different, which can intercept the corresponding pollutants and block on one side of the membrane. Membrane treatment technology not only acts on large particles of impurities, but also has good retention effect for some microorganisms and bacteria, so it can greatly improve the safety of water. However, membrane treatment technology also has some defects, such as high cost, easy to plug, etc. membrane pollution is also the biggest problem of membrane treatment technology, which limits the development of membrane technology. From 1950 to 2006, China’s drinking water quality standard has been revised for six times. The currently implemented drinking water standard is “drinking water quality standard” (GB 5749-2006), with a total of 106 indicators, including 42 conventional indicators and 64 unconventional indicators, to ensure the safety of water quality. Qualified tap water from the water plant to the faucets of residents’ homes also passes through the water supply pipe network and secondary water supply facilities, such as high-rise water towers and water tanks. In order to ensure the microbial safety of tap water and inhibit the re breeding of bacteria in the water, a certain amount of residual chlorine will be added to the produced water to continuously disinfect the water supply pipe network, so as to ensure that the tap water will not be polluted again during the “long journey” Dye. < p > < p > according to the “sanitary standard for drinking water” (GB5749-2006), the total residual chlorine standard of the water plant is 0.5-3.0mg/l, and the residual chlorine value at the end of the pipe network is not less than 0.3mg/l. Therefore, it is normal for tap water to have a slight chlorine smell. During the boiling process of tap water, the residual chlorine will be volatilized, so there is no need for extra standing. < / P > < p > sometimes the tap water from the tap is light yellow or milky white. Especially after the water is cut off, the tap water will be particularly turbid. Is such tap water still safe? < / P > < p > the tap water will be light yellow, which may be due to the long-term use of pipes and taps, the presence of rust, or the construction of water supply sections. In general, turn on the tap and put water for a while. At present, most of the newly laid water supply pipes are made of plastic pipes, high-quality cast iron pipes and stainless steel pipes which are not easy to rust. Therefore, the Yellow situation of tap water has been greatly reduced. < / P > < p > and sometimes we will find that the tap water at home is cloudy and milky white, accompanied by many small bubbles. This is due to the secondary pressure of the water supply system, the dissolved gas will decompose into tiny bubbles by pressure, resulting in the water looks milky white. In fact, after a few minutes of static, the bubbles will disappear and the water quality will become clear, which will not affect the water quality. When it comes to the drinking safety of tap water, we have to mention the hot water purifier in recent years. With the development of society, our pursuit of quality of life is increasing, and we also want to use higher quality water, “do you want to install a water purifier? What brand of water purifier should be installed? What are the functions of water purifiers? ” And so on. Water purifier, in fact, is to make qualified tap water better, so water purifier can be required, but it is not necessary. < / P > < p > there are many kinds of water purifiers on the market, and their prices vary greatly. In order to understand the function and effect of household water purifier, it is necessary to understand its process principle. At present, the mainstream household water purifier on the market is a composite water purifier, which is mainly composed of ppcotton (primary filtration), activated carbon or other composite adsorption materials (secondary filtration), and membrane materials (core filtration) in series to achieve the purpose of adsorbing impurities. < / P > < p > in addition, there are also softened water purifiers that can reduce the hardness of water. The main components of scale are calcium carbonate and magnesium carbonate. The more scale in water, the higher the content of calcium and magnesium ions. Such water is commonly known as “hard water”. Hard water boiled rice, tea will taste worse. Softening water purifier is based on the composite water purifier with anion / cation exchange resin components, which can remove calcium and magnesium plasma in water, reduce water hardness, and improve taste and performance. < / P > < p > the water purifier can play a certain role in further improving the safety and taste of tap water. However, it should be noted that the process of adsorption and retention of microorganisms by water purifier components is a physical function, and will not completely kill the microorganisms. If the filter element is not replaced or used improperly, the microorganisms will proliferate again in the activated carbon and membrane module It brings more serious secondary pollution. The progress of science and technology can make us drink more hygienic and safe tap water and make life more convenient. We should also understand the precious water resources and the hard won clean water. Protecting water sources and saving water is something that everyone should bear in mind and strive to practice. Spontaneous combustion at a Guangzhou Motor vehicle intersection and other traffic lights in Shenzhen