The faucet in the home kitchen is one of the main products of the bathroom water supply. The water flowing out of the faucet is either heated for drinking, cooking, brushing teeth, washing vegetables, fruits, and clothes, which is closely related to people's daily life. As people pay more and more attention to health and food safety, the precipitation and precipitation indicators of heavy metal ions in water from faucets have become important environmental health and safety indicators that people and the industry care about.

1. Precipitation of heavy metals from faucets
⑴. Precipitation of heavy metal ions. The faucet is composed of materials such as metal, ceramics and plastics. The metal contains a lot of heavy metals such as zinc and copper. A small amount of lead added during processing is segregated on the inner and outer surfaces of the faucet. The water in the faucet will destroy the surface of the lead washing, forming "corrosion", and the lead ions inside are exposed, resulting in a certain degree of lead precipitation and dissolution into the water, especially the "overnight water" retained in the water pipe, which has a higher content of heavy metals.
⑵. Heavy metal ion precipitation index. It refers to soaking water prepared with close to real tap water components under the condition of eliminating the interference of heavy metals and other harmful components, and using soaking water according to the soaking procedures and methods specified in the standard to soak the surfaces in the faucet that are in contact with water. Finally, the precipitation of heavy metals in the soaking water was tested. The heavy metal precipitation index has a great correlation with the mass percentage of the faucet manufacturing raw materials. Usually, the level of the heavy metal mass percentage will determine the level of the precipitation index.
3. Relevant standards for heavy metal precipitation
①.Basic standard. GB 5749-2006 "Standard for Drinking Water" is a full-text mandatory national standard, which includes the sanitary requirements for drinking water quality in my country and the sanitary requirements for sanitary and safe products of drinking water.
③. Product standards. Mainly include: GB18145 "Ceramic Sheet Sealing Faucet", QB1334 "General Technical Conditions for Faucet". GB18145 "Ceramic Sheet Sealing Faucets" is a national standard with some mandatory provisions. In the 2003 edition, there is no mandatory requirement for heavy metal precipitation indicators, but mandatory provisions have been made in the latest revised standard draft for approval; QB1334 "General Technical Conditions for Faucets" is part of the It is a mandatory industry standard. In the 2004 version, there was no mandatory requirement for heavy metal precipitation indicators, and the newly released 2013 version of the standard has become a recommended standard.
The relationship between the three standards: According to the requirements of the basic standard, the product standard puts forward clear regulations on the precipitation index of heavy metals and the corresponding test methods. The corresponding method standard will be referenced in the product standard
2. Heavy metal precipitation experiment in faucet
The precipitation of heavy metal ions in faucets causes changes in trace elements in tap water, which has a significant impact on the quality of people's drinking water. In order to avoid harm to the human body and provide a scientific basis for the formulation of sanitary and safety standards for drinking water wading products, the iron (Fe), zinc (Zn), manganese (Mn) in the water pipes of indoor taps were measured by atomic absorption spectrophotometry overnight. , copper (Cu) content was measured and analyzed.
2.1 Instruments and materials
WFX-ID atomic absorption spectrophotometer, iron, zinc, copper, manganese hollow cathode lamp. In the urban area, rooms in different areas were randomly selected, and 12 faucets of two types of indoor cast iron and chrome-plated (inner layer galvanized) faucets were selected to test their water quality.
2.2 Methods
According to the national standard of the People's Republic of China GB5750-1985 "Standard Test Methods for Drinking Water", atomic absorption spectrophotometry was used to determine iron, zinc, copper and manganese in water.
3 Discussion
The cast iron faucet is made of iron. Due to the rust of the faucet, the tap water is stagnant and stored for one night in it, resulting in a significant increase in the iron content, the tap water has a rust smell, and the chroma (yellow) and turbidity increase. The water from the chrome-plated faucet is stagnant and stored in the galvanized faucet overnight, and the friction of the opening and closing faucet increases the zinc content, and causes the water turbidity to increase, and there is an unpleasant metallic smell. The pollution degree of iron and zinc in the water of the cast iron and chrome-plated faucets is related to various factors such as the corrosion of the faucet, the degree of wear of the gasket and the difference in the production process, and also has a certain relationship with the water pipe (galvanized iron pipe).
The survey results show that the iron and zinc content in the head water of cast iron and chrome-plated faucets are negatively correlated with the water output. When the flow reaches 3L, the iron and zinc content basically meets the drinking water quality standards. In daily life, although the sensory properties of the water from the water pipe overnight are poor, it has not attracted people's attention.
4. Conclusion
Due to the different faucet materials and the synergistic effect of tap water pipes, the chromaticity and turbidity of the water in the overnight water head exceeded the standard, and the content of iron and zinc in most of the water head exceeded the standard, which affected the water quality of the tap water. It is suggested to turn on the faucet in the morning, and the first 3 to 5L of the overnight tap water is not suitable for drinking, but can be used as domestic water. It is recommended to promote the use of high-quality and safe drinking water supply pipes and faucets and other wading products.
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