If the tap water is qualified, do you still need to install a water purifier?

The movie "Mermaid" has a saying, "if you can't drink a glass of clean water and breathe a breath of clean air, no matter how much money you make, you will die.".
Yes, once clean water, once the source of life, but now we need to be cautious.
Therefore, many families have installed water purifiers to ensure the safety of drinking water for their families. However, some people think that the tap water at home is qualified after being treated by the waterworks. If the water purifier is installed again, it is a kind of repeated investment and unnecessary consumption.

For this problem, users who have installed a water purifier and changed the filter element will know that the original clean filter element is covered with yellow sand and other pollutants after a period of use. If there is no water purifier, these visible and invisible harmful impurities will be drunk into the body.
So where do these pollutants come from?

The first is the water pipe network. When the tap water is transported or stayed in the water supply network for a long distance after leaving the factory, there will be various problems when it reaches the user's place. Especially for the water pipes with long service life, aging and corrosion problems will inevitably occur after a long time of use. The problems of yellow water quality, sediment and rust in many areas are water pollution caused by water pipe aging.
The second is the pollution caused by the secondary water supply tower and water tank. If the water tank of some high-rise residential areas is not cleaned for a long time, it will store a lot of pollution impurities. Long term accumulation will lead to serious pollution of tap water, and the tap water delivered to each household can not meet the standard of direct drinking.

First of all, the standard of tap water is set to take into account the actual water quality of our country. It is the most basic safety line. Figuratively speaking, the qualified standard of tap water is equivalent to 60 points in the examination, which is only a passing line.
Secondly, 106 indicators of tap water can not completely exhaust all kinds of harmful elements to human body, just common harmful substances. Therefore, even if all 106 indicators are qualified, there is no guarantee that there are more than 106 indicators of harmful substances.
Third, the safety standard of tap water is based on statistical data, which is a basic guarantee line of safety. In real life, because of individual physical differences, everyone's tolerance to harmful substances is different. For those whose tolerance is lower than the average level, the safe content for the vast majority of people may be dangerous or even fatal to them.

Fourth, the role of some harmful substances is gradually accumulated, such as heavy metals. Even if the safe dose of harmful substances, accumulated in the body to a certain amount, will also cause disease.
Fifth, there is always residual chlorine in tap water, because chlorine is intentionally added into tap water process, and residual chlorine is harmful to human health. Therefore, if you want to drink 100 points of high-quality water, tap water is obviously not the best choice, and it should be further purified
It seems that even qualified tap water needs to be purified.