What is groundwater? Why is it important? Water is the most important resource to humans. It is essential for the existence of all forms of life. Although an ocean of water covers the earth, it is important to remember that there is no new water. The earth only contains and redistributes a certain amount. Groundwater is water below the earth’s surface in rock, sand, gravel and soil. The rainfall that enters the ground keeps up the water level. Surface water and groundwater are the two main sources for drinking water. Nearly 50 percent of the U. S. population and 95 percent of rural homes depend on groundwater for their drinking and water supply. In Missouri, 67 percent of the population gets its water from surface water, while 33 percent depend on groundwater supplies. We need clean, usable groundwater to maintain an adequate and safe supply of drinking water. So we must manage our groundwater wisely so that it does not become polluted by human activities.