Many people receive their water from water treatment facilities and water towers. Water, however, is a natural resource, so its true sources are also natural, and typically include icecaps, rivers, and oceans. When people receive their water by way of pipes or wells, they should understand that these are a distribution mechanism instead of a source.
Earth’s largest water source is the oceans. There are five oceans: the Atlantic, Pacific, Indian, Southern, and Arctic. Together they contain about 97% of Earth's water. This is saltwater, which is beneficial to humans for many things, such as traveling and maintaining natural cycles, but it is not useful for drinking. Consuming saltwater can actually be very harmful to humans.
The majority of freshwater is frozen, mainly in the form of glaciers and icecaps. A glacier is a large body of slowly moving frozen water that, if it were instantly melted, would be converted into a river. An icecap is a miniature sheet of ice found at high elevation, such as in the mountains. Other frozen water sources include permanently frozen ground, or permafrost; icebergs; and ground ice.
These frozen water sources can affect the sea levels. If wide scale melting occurred, Earth’s water levels would increase and the land area would decrease. It is commonly believed that at different points in history, when the climates were different, the levels of the various sources of water were also different.
The second largest freshwater source is groundwater, which is water that lies under the surface of the land. It exists almost everywhere in the world, although, in some places, a person would have to dig quite deep to access it. This water may be accessible in other locations, but it may not be healthy for human consumption if it is not treated.
The level of groundwater is supplied, in part, by precipitation. When rain falls, for example, it sinks down into the ground. It is often collected in aquifers, which are natural water storage compartments formed between the rocks under the surface. Groundwater is an important water source for human consumption.
Most of the water that people use, however, comes from rivers, which falls into a category known as surface water. This category is represented mainly by lakes, but it also includes swamps. Surface water represents the smallest amount of water on Earth.