Why can't you drink tap water even if it's boiled?

The main process of producing tap water in a water plant can be divided into several parts, such as water extraction, dosing, coagulation, sedimentation, filtration and water supply. Therefore, from the water plant to send out the tap water is cleaner. So why can't tap water be drunk directly?

Original A, in order to disinfect the tap water, the water plant will often add a small amount of chlorine in the water, chlorine dissolved in water will generate hypochlorous acid and other substances, hypochlorous acid has a very strong sterilization, bleaching effect. But at the same time, the water will produce some hypochlorite and organic chlorine, they are called residual chlorine. Residual chlorine has strong oxidizing properties, if you often drink tap water containing residual chlorine, it is obviously not good for health. However, the residual chlorine in tap water is an unstable substance, which can be easily decomposed and volatilized under the action of light or heat. Therefore, after the tap water is boiled, the residual chlorine in it can be removed.

In addition, the tap water output from the water plant has to pass through many pipes before it can be delivered to thousands of households. These pipes are inevitably some unclean substances and disease-causing bacteria, tap water is likely to be formed in the delivery process of secondary pollution. Such secondary contamination of tap water, if not thoroughly boiled and disinfected, it is easy to infect people with a variety of diseases. Therefore, tap water is not directly drinkable.