Because the water in the cave is not natural water. The water quality is polluted in the places it passes through and the calcium carbonate is so strong that drinking it causes stomach upset.
Groundwater pollution is the deterioration of groundwater quality caused by human factors. The main causes of groundwater pollution are: industrial wastewater is discharged directly underground, contaminated surface water invades the groundwater, human and animal excreta or contaminated water due to excessive use of pesticides occurs. infiltrate into the ground, etc.
The result of pollution is an increase in the content of harmful components such as phenol, chromium, mercury, arsenic, radioactive substances, bacteria, organic matter, etc. in groundwater. Contaminated groundwater is harmful tohuman health and industrial and agricultural production.
Detailed information:
Depending on its development and evolution, karst can be divided into the following six types.
2) Surface water infiltrates and dissolves downward along cracks in the limestone, forming sinkholes when the depth exceeds 100 m.
3) Groundwater falling from the sinkhole flows laterally toward the aquifer, forming a cave.
4) With the formation of underground caves, the surface of the earth collapses. If the depth of the collapse is large but the area is small, it is called a collapse funnel. If the depth is small but. the area is small, it is called a sinkhole.
5) Dissolution and collapse of groundwater combine over a long period of time to form sloping valleys and natural bridges.
6) As the ground rises, caves and underground riversoriginal are lifted from the surface and become dry valleys and stone forests. Groundwater dissolution continues beneath ancient caves and underground rivers. The stone forest south of the Yunnan Road is the product of the first stage (the ravine stage) mentioned above. The natural landscape here has become particularly beautiful thanks to the moving legend of Ashima.
The elephant trunk hill in Guilin was formed when the original course of the underground river was exposed to the surface. In Guangxi, you can often see such caves rising above the surface, commonly called "goddess mirrors" or "fairy mirrors".