Tap water contains scale, which is harmful to health. Scale is a hard deposit formed on the wall of water pipes, mainly calcium carbonate and calcium silicate, and may also contain metal ions such as water iron, water zinc and water aluminum. Heavy metal ions, corrosive gases and organic substances in scale will pollute water quality, affect the taste and taste of tap water, destroy the microbial activity in water and affect the sanitary quality of water. Heavy metal ions in scale may also enter the human body through drinking tap water, which has a negative impact on human health, especially on the health of children and infants.