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Groundwater is water that comes from the ground. Sounds easy, doesn't it? Amazingly, many people use groundwater but don't even know it. In fact, half of everyone in the United States drinks groundwater everyday! Groundwater is even used to irrigate crops which grow food for tonight's dinner.
Where does ground water come from? Groundwater comes from rain, snow, sleet, and hail that soaks into the ground. The water moves down into the ground because of gravity, passing between particles of soil, sand, gravel, or rock until it reaches a depth where the ground is filled, or saturated, with water. The area that is filled with water is called the saturation zone and the top of this zone is called the water table. Makes sense, doesn't it? The top of the water is a table! The water table may be very near the ground's surface or it may be hundreds of feet below.
Think about this: have you ever dug a hole in sand next to an ocean or lake? What happens? As you're digging, you eventually reach water, right? That water is groundwater. The water in lakes, rivers, or oceans is called surface water... it's on the surface. Groundwater and surface water sometimes trade places. Groundwater can move through the ground into a lake or stream. Water in a lake can soak down into the ground and become groundwater.
Groundwater is stored in the ground in materials like gravel or sand. It's kind of like the earth is a big sponge holding all that water. Water can also move through rock formations like sandstone or through cracks in rocks. An area that holds a lot of water, which can be pumped up with a well, is called an aquifer. Wells pump groundwater from the aquifer and then pipes deliver the water to cities, houses in the country, or to crops.
Most groundwater is clean, but groundwater can become polluted, or contaminated. It can become polluted from leaky underground tanks that store gasoline, leaky landfills, or when people apply too much fertilizer or pesticides on their fields or lawns. When pollutants leak, spill, or are carelessly dumped on the ground they can move through the soil. Because it is deep in the ground, groundwater pollution is generally difficult and expensive to clean up. Sometimes people have to find new places to dig a well because their own became contaminated.
When the water reaches the earth's surface, some of it will flow along the surface of the earth as runoff while the rest of it soaks into the soil--called recharge. Down, down, down the water goes through the soil until it becomes groundwater and is stored in the aquifer below. Once the water has joined the aquifer, it doesn't stop there. The groundwater slowly moves through spaces and cracks between the soil particles on its journey to lower elevations. This movement of water underground is called groundwater flow. Eventually, after years of underground movement, the groundwater comes to a discharge area where it enters a lake or stream. There, the water will once again be evaporated and begin the cycle again. Water has been transported through the water cycle for millions of years and will continue this cycle forever.
Click on Water Facts and test your water knowledge.
Water is a precious resource for all living things. Even animals that live in the desert need water. They derive their water sources from the plants they eat, streams, and natural pools of water.