Most of the world's water supply is saltwater stored in the oceans. Converting saltwater to freshwater is generally too expensive to be used for industrial, agricultural or household purposes. The type of water we generally use in human activities is freshwater. Surface water is water that is visible above the ground surface, such as creeks, rivers, ponds and lakes. Ground water is water that either fills the spaces between soil particles or penetrates the cracks and spaces within rocks.
Most people get their water from ground water sources.
Millions more get their water from private wells which also tap ground water sources. Ground water systems tend to serve smaller numbers of people, while surface water systems generally serve large populations. The quantity and quality of the world's water supply depends on how we choose to use water. Nonconsumptive use returns water, polluted or not, to the system. Creating hydroelectric power is an example of nonconsumptive use.