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According to the US Geological Survey, 50% of people's fresh water comes from the groundwater found in wells. In rural
areas, that rises to 90%. Traditionally, water resource agencies and scientists used only the data gathered by traditional
methods to develop water usage models or to determine actual local usage. In 2002, NASA and the German Space Agency
launched the Gravity Recovery and Climate Experiment (GRACE) mission to measure changes in the Earth's gravity. Slight
changes in the distance between the twin GRACE satellites as they pass over Earth's features indicate changes in Earth's
gravitational field. Scientists can then track differences in the Earth's gravity field from data retrieved from the GRACE
satellites, improving their understanding of how water is moving and cycling around the planet. [Source: NASA Earth System Science Data and Services]
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