Why does rainwater gradually turn green after collection?

Water will turn green if it is left for a long time, because algae in the water multiply.

As long as any water is exposed to the air for a long time, algae spores contained in the air will enter the water with the circulation of the air, and algae spores will produce photosynthesis when they meet sunlight, and then algae will be produced, and they will continue to multiply in large numbers through photosynthesis. The water is full of tiny algae, which makes it look green.

The rain solar term generally starts from February 18 to 20 and ends on March 4 or 5.

In rainy and solar terms, the direct point of the sun is gradually approaching the equator from the southern hemisphere. At this time, the sunshine hours and intensity in the northern hemisphere are increasing, and the temperature is rising rapidly. Warm and humid air from the ocean becomes active and gradually pushes northward to meet with cold air, forming rainfall. The rainy season is changeable, which is one of the seasons with the most cold wave processes in the whole year, with cold and hot, warm and cold at first.

In ancient times, rainwater was divided into three stages: "One stage was that Rex sacrificed fish; Second, wait for Hongyan to come; Third-class grass sprouted. " Rain in the "July 9" period, the river broke the ice and the geese returned to the north. Folk customs related to rain mainly include "mending the sky and wearing it", "protecting the sky" and "bumping into worship and sending it away".