How is freshwater on land replenished

But, the Earth cleans and replenishes the water supply through the hydrologic cycle. The earth has an abundance of water, but unfortunately, only a small percentage about 0. The other Still, much of the 0. Most of the water used by humans comes from rivers. The visible bodies of water are referred to as surface water.

The majority of fresh water is actually found underground as soil moisture and in aquifers. Groundwater can feed the streams, which is why a river can keep flowing even when there has been no precipitation.

Humans can use both ground and surface water. Surface water is far easier to reach, so this becomes the most common source of potable water. About billion gallons per day of surface water is used by humans. About 77 billion gallons of groundwater are used each day. Problems also exist in contamination of the water supplies.

This further limits the amount of water available for human consumption. Water is found in many different forms and in many different places. While the amounts of water that exist seem to be plentiful, the availability of the water for human consumption is limited. Surface waters can be simply described as the water that is on the surface of the Earth.

This includes the oceans, rivers and streams, lakes, and reservoirs. Surface waters are very important. They constitute approximately 80 percent of the water used on a daily basis. In , the United States alone used approximately , billion gallons of surface water a day. Surface waters make up the majority of the water used for public supply and irrigation. It plays less of a role in mining and livestock industries.

Oceans, which are the largest source of surface water, comprise approximately 97 percent of the Earth's surface water. However, since the oceans have high salinity, the water is not useful as drinking water. Efforts have been made to remove the salt from the water desalination , but this is a very costly endeavor. Salt water is used in the mining process, in industry, and in power generation. The oceans also play a vital role in the hydrologic cycle, in regulating the global climate, and in providing habitats for thousands of marine species.

Rivers and streams constitute the flowing surface waters. The force of gravity naturally draws water from a higher altitude to a lower altitude.

Rivers obtain their water from two sources: groundwater, and runoff. Rivers can obtain their water from the ground if they cut into the water table, the area in which the ground is saturated with water. This is known as base flow to the stream.

Runoff flows downhill, first as small creeks, then gradually merging with other creeks and streams, increasing in size until a river has formed. These small creeks, or tributaries, where the river begins are known as the headwaters. Springs from confined aquifers also can contribute to rivers.

A river will eventually flow into an ocean. A river's length can be difficult to determine, especially if it has numerous tributaries. The USGS Web site defines a river's length as "the distance to the outflow point from the original headwaters where the name defines the complete length.

The land that is upgradient of any point on the river is known as the drainage basin or watershed. Ridges of higher land, such as the Continental Divide, separate two drainage basins.

Flowing water is extremely powerful and plays an important role in creating the landscape and in humans' lives. Flowing water is used for numerous reasons including irrigation and hydroelectric power production. Rivers erode the landscape and change the topography of the Earth by carving canyons and transporting soil and sediment to create fertile plains.

Rivers carry soil and sediment that have been washed into the river when it rains or snow melts. The faster the water moves, the larger the particle size the river is capable of carrying. The USGS measures how much sediment a river carries by measuring the streamflow, or the amount of water flowing past a given site; and the sediment concentration.

Sediment in the river can be helpful and harmful. Condensation is the process of water vapor turning back into liquid water, with the best example being those big, fluffy clouds floating over your head. And when the water droplets in clouds combine, they become heavy enough to form raindrops to rain down onto your head. You can't see it, but a large portion of the world's freshwater lies underground. It may all start as precipitation, but through infiltration and seepage, water soaks into the ground in vast amounts.

Water in the ground keeps all plant life alive and serves peoples' needs, too. Note: This section of the Water Science School discusses the Earth's "natural" water cycle without human Runoff is nothing more than water "running off" the land surface. Just as the water you wash your car with runs off down the driveway as you work, the rain that Mother Nature covers the landscape with runs off downhill, too due to gravity.

Runoff is an important component of the natural water cycle. Skip to main content. Search Search. Water Science School. Freshwater Lakes and Rivers and the Water Cycle. The Components of the Water Cycle Investigate each part of the water cycle adults and advanced students Learn more.

Science Center Objects Overview Related Science Freshwater on the land surface is a vital part of the water cycle for everyday human life. Lakes are valuable natural resources, both for human and non-human life. One estimate of global water distribution. Water source Water volume, in cubic miles Water volume, in cubic kilometers Percent of total water Percent of total freshwater Fresh groundwater 2,, 10,, 0.

More topics and other components of the water cycle:. Date published: July 10, Filter Total Items: Year Select Year Apply Filter.

Date published: November 6, Note: This section of the Water Science School Date published: September 8, Date published: July 16, Date published: June 12, Note: This section of the Water Science School discusses the In addition to rivers, lakes can also be an excellent source of freshwater for human use. They usually receive water from surface runoff and groundwater discharge. They tend to be short-lived on a geological time-scale because they are constantly filling in with sediment supplied by rivers.

Lakes form in a variety of ways including glaciation, recent tectonic uplift e. People also create artificial lakes reservoirs by damming rivers. As Earth was coming out of the last Ice Age about 15, years ago, the climate in the western U. Although glaciers represent the largest reservoir of fresh water, they generally are not used as a water source because they are located too far from most people Figure 7.

Melting glaciers do provide a natural source of river water and groundwater. Over the past century, sea level has been rising in part due to melting glaciers. Although most people in the world use surface water, groundwater is a much larger reservoir of usable fresh water, containing more than 30 times more water than rivers and lakes combined. Groundwater is a particularly important resource in arid climates, where surface water may be scarce.

Groundwater is water located in small spaces, called pore space , between mineral grains and fractures in subsurface earth materials rock or sediment. Most groundwater originates from rain or snowmelt, which infiltrates the ground and moves downward until it reaches the saturated zone where groundwater completely fills pore spaces in earth materials.

Other sources of groundwater include seepage from surface water lakes, rivers, reservoirs, and swamps , surface water deliberately pumped into the ground, irrigation, and underground wastewater treatment systems septic tanks.

Recharge areas are locations where surface water infiltrates the ground rather than running into rivers or evaporating. Wetlands, for example, are excellent recharge areas. A large area of sub-surface, porous rock that holds water is an aquifer. Aquifers are commonly drilled, and wells installed, to provide water for agriculture and personal use. People need water, oftentimes large quantities, to produce the food, energy, and mineral resources they use.

Human beings require only about 1 gallon per day to survive, but a typical person in a U. The water demand of an area is a function of the population and other uses of water. Figure 9. Red line gives U. Source: United States Geological Survey Global total water use is steadily increasing at a rate greater than world population growth Figure During the 20th century global population tripled and water demand grew by a factor of six.

The increase in global water demand beyond the rate of population growth is due to improved standard of living without an offset by water conservation. Rainwater is collected in a 20, litre tank below the building and is used for showering and toilet flushing. In October we had storms that led to a lot of flooding; the University was flooded in several different buildings.

Due to cost pressures, business could be an even greater driver of water efficiency than governments. Anders Berntell believes that "many of the big multinational companies are way ahead of governments when it comes to understanding and acting on the challenges that we are facing. Thermal power sources [nuclear, coal, natural gas] require vast amounts of water for cooling. Renewables for the most part — solar and wind — do not. It all has to do with policies to encourage, incentivise, and invest.

Whichever effective model of conserving freshwater we come up with, we need to come up with one — and sooner rather than later. If you liked this story, sign up for the weekly bbc. Future Now. Future Now Water. Is the world running out of fresh water?