When looking at the Earth from the outer space, you will find it is a blue planet. This has been widely accepted. The 70-percent surface of the Earth is covered by ocean, but in fact this planet is not as moist as we think. We should avoid to be deceived by what we take for granted. The average radius of the Earth is 6378 kilometers. The average thickness of its crust is 17 kilometers. The average depth of all oceans is 3.2 kilometers, which is even not up to the odd depth of the earth’s crust. If the Earth is assimilated to an apple, the water covering the planet is even thinner than the peel of apple. Among this, the water we can use is much less than what we assume. The fresh water we can depend on for daily life only accounts for less than 1% of all water on the Earth, much of them being stored in the rivers and lakes or underground. According to World Water Development Report 2022 published by UN, the total amount of ground water accounts for 99% of the total fresh water in a liquid state on the Earth, while the fresh water in the forms of river and lake only accounts for 1%. For mostly accumulating in the soil or rock beneath our feet and being hard to be seen and touched, the ground water is often to be neglected. How is ground water formed? How can we utilize it? Today let’s disclose the ins and outs of ground water.