Some water source pollutants can cause diseases. Water source pollution is a common problem in the world. With the development of industry, the discharge of domestic sewage and industrial wastewater, as well as the use of pesticides and fertilizers in agriculture, the types and quantity of impurities in water sources are increasing, and the water quality is deteriorating.
China's current drinking water health standard GB5749-2006, water quality indicators increased from 35 items in gb5749-85 (1985) to 106 items, the increase in the number of control indicators shows that people attach great importance to the safety of water sources.

According to the existing detection technology, 2221 kinds of organic matter have been found in the main rivers, rivers and lakes in China, and 765 kinds of organic matter have been found in drinking water. Some are carcinogenic, teratogenic and mutagenic pollutants, which have acute or chronic, direct or indirect toxic effects on human body.

The natural water environment is a large circulation system, and some local pollution of water source will diffuse through circulation. The water quality of some local water sources is still not optimistic.

You think "the water quality here is better", the judgment basis is the naked eye observation, the clear water is good water. In fact, the naked eye can only see more than 50 microns of particles in the water, and there are many fine particles, colloids and various pollutants dissolved in the water that your eyes can't see.