Surface and Groundwater
The water in the world is divided into two types: surface and groundwater. Surface water is found in lakes, rivers, and streams and is tapped for use by the public. Groundwater must be pumped out of natural underground storage areas called aquifers after drilling.
Surface water is called 'soft' water because it does not contain many minerals. It can be contaminated in many ways. Pesticides, animal wastes, industrial waste, and insecticides can all contribute to making the water less than pure, even in streams flowing down from the mountains which are usually considered to carry 'pure' water.
Groundwater is contained below the surface of the ground by soil or rock. Rivers that flow beneath the ground, rain and melting snow replenish the aquifers. Groundwater may contain all the same contaminants as surface water in addition to the minerals it adds from below the ground. Rock does act as a filter, though, so groundwater does usually contain less pollution. The contaminants in groundwater are much more difficult to clean up than those in surface water, however.
As rain falls onto the ground, plants use some of the nutrients. The rain goes into the soil, filtering down through clay, rock, and soil. Finally, this water reaches an aquifer or could be trapped between levels of rock and create a water table. This type of water is found in wells. Groundwater is called 'hard' water because of the minerals it takes in while filtering down through the soil.
Groundwater is used for drinking and other household needs. Surface water may have the same uses but may be used also in agriculture and the generation of electricity. The surface water can replenish the groundwater as the rain filters down. Surface water can evaporate while groundwater does not, as it is not exposed to the sun. Groundwater retains the same temperature all the time. Surface water takes the temperature of its surroundings. It will be warmer in summer than in winter.
Surface water contains less salt than groundwater. The deeper the water is, the higher the content of salt. Groundwater contains more minerals. It does not have any disease-causing organisms, like salmonella and malaria. Both groundwater and surface water contains many contaminants.
Groundwater is extracted from the ground for use by drilling wells. It is usually cheaper and easier to use groundwater for a public water supply. In the United States, groundwater provides the greatest amount of usable water for public use. California yearly withdraws the largest amount of groundwater of all the states. Many public water supplies use groundwater totally. The reservoirs of groundwater contain more water than all the surface water in the United States combined.
Groundwater makes up about twenty percent of the world's fresh water supply. It is a very important part of maintaining a supply of water during a time of drought. Groundwater is held in long-term reservoirs. The Great Artesian Basin in eastern and central Australia is one of the largest confined aquifers in the world.
Overuse of groundwater can result in a lowering of the water table below where an existing well can tap into it. Therefore, deeper wells are needed. When too much water is pumped out from underground aquifers, subsidence results. The land looks like it has little craters. A drop in the ground surface occurs. The city of New Orleans is below sea level partly because of the removal of water from the aquifer systems below it. It has experienced subsidence.
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