Ground water is the water in rock voids that below the surface. In a narrow sense, it refers to the water in saturated aquifers below the underground water surface. Ground water is the various forms of gravity water buried below the surface.

There are three definitions in foreign studies.

The first one: it refers to all water buried in groundwater that is significantly different from surface water, especially the part of water in the saturated zone of an aquifer. The second one is that flowing or permeating downward, saturating the soil and rocks and replenishing the water of springs and Wells; The third is the water stored in underground rock cavities, in gaps that make up the earth's crust material.

Groundwater is an important part of water resources. Due to its stable and good quality, it is one of the important water sources for agricultural irrigation, industrial mining and urban development. However, the change of groundwater will also cause swamping and salinization if under certain conditions.

Ground water generally refers to water in the underground porous medium, which includes pore medium, medium and karst medium.

The current pollution situations

Under the action of air pollution, domestic sewage, factory discharge and other pollution sources, the pollution of shallow groundwater is becoming serious and fast.

The drinking water sources and surface water in rural areas are polluted to different degrees, the outstanding performance is the increasing pressure of industrial and mining pollution, the intensified local domestic pollution, and serious pollution from livestock and poultry breeding.

The level of contaminated groundwater

Class I: Good water quality. Groundwater only needs disinfection treatment, and surface water can be provided for drinking after simple purification treatment (such as filtration) and disinfection.

Class II: Water quality is slightly polluted. After conventional purification treatment (such as flocculation, precipitation, filtration, disinfection and other processes), the water quality can be used for drinking.