Rain water's most well-known and most important effect is providing you with water to drink. According to the United States Geological Survey, rain water seeps into the ground in a process called infiltration. Some of the water seeps deep beneath the top layers of soil where it fills up the space between subsurface rocks--it becomes ground water, also called the water table. Less than 2 percent of the earth's water is ground water, but it provides 30 percent of our fresh water. Without rain water's continued replenishment of the water table, potable water would become scarcer than it already is.