All the Water in the World

The image show blue spheres representing relative amounts of Earth's water in comparison to the size of the Earth. Are you surprised that these water spheres look so small? They are only small in relation to the size of the Earth. These images attempt to show three dimensions, so each sphere represents "volume." They show that in comparison to the volume of the globe, the amount of water on the planet is very small. Oceans account for only a "thin film" of water on the surface.

The largest sphere represents all of Earth's water. Its diameter is about 860 miles (the distance from Salt Lake City, Utah, to Topeka, Kansas) and has a volume of about 332,500,000 cubic miles (mi3) (1,386,000,000 cubic kilometers (km3)). This sphere includes all of the water in the oceans, ice caps, lakes, rivers, groundwater, atmospheric water, and even the water in you, your dog, and your tomato plant.





Where it is Found

In the first bar, notice how only 2.5% of Earth's water is freshwater - the amount needed for life to survive.

The middle bar shows the breakdown of freshwater. Almost all of it is locked up in ice and in the ground. Only a little more than 1.2% of all freshwater is surface water, which serves most of life's needs.

The right bar shows the breakdown of surface freshwater. Most of this water is locked up in ice, and another 20.9% is found in lakes. Rivers make up 0.49% of surface freshwater. Although rivers account for only a small amount of freshwater, this is where humans get a large portion of their water from.

It is all Connected

The water cycle has no starting point, but we'll begin in the oceans, since that is where most of Earth's water exists. The sun, which drives the water cycle, heats water in the oceans. Some of it evaporates as vapor into the air; a relatively smaller amount of moisture is added as ice and snow sublimate directly from the solid state into vapor. Rising air currents take the vapor up into the atmosphere, along with water from evapotranspiration, which is water transpired from plants and evaporated from the soil. The vapor rises into the air where cooler temperatures cause it to condense into clouds.

Air currents move clouds around the globe, and cloud particles collide, grow, and fall out of the sky as precipitation. Some precipitation falls as snow and can accumulate as ice caps and glaciers, which can store frozen water for thousands of years. Snowpacks in warmer climates often thaw and melt when spring arrives, and the melted water flows overland as snowmelt. Most precipitation falls back into the oceans or onto land, where, due to gravity, the precipitation flows over the ground as surface runoff. A portion of runoff enters rivers in valleys in the landscape, with streamflow moving water towards the oceans. Runoff, and groundwater seepage, accumulate and are stored as freshwater in lakes.

Not all runoff flows into rivers, though. Much of it soaks into the ground as infiltration. Some of the water infiltrates into the ground and replenishes aquifers(saturated subsurface rock), which store huge amounts of freshwater for long periods of time. Some infiltration stays close to the land surface and can seep back into surface-water bodies (and the ocean) as groundwater discharge, and some groundwater finds openings in the land surface and emerges as freshwater springs. Yet more groundwater is absorbed by plant roots to end up as evapotranspiration from the leaves. Over time, though, all of this water keeps moving, some to reenter the ocean, where the water cycle "ends" ... oops - I mean, where it "begins."



What is a Watershed

A watershed is an area of land that contains streams and rivers that all drain into a single body of water, such as a lake or the ocean. Watersheds can be big or small, but they all have high points like ridges and mountains that capture water, store it, and eventually release it downhill. Many of our actions impact watersheds, and as the rivers and streams flow downstream through communities, the ocean becomes the final resting place for much of the pollution and contaminants that these rivers and streams are carrying.


North American River Basins

A beautiful map of the river basins of the US made by  Imgurian Fejetlenfej.  Of the 50 United States, 23 are coastal and seven (7) are along the great lakes.  Of the remaining inland 20 states four (4) are along the continental divide; Montana, Wyoming, Colorado and New Mexico, four (4) are western; Idaho, Utah, Nevada and Arizona, eight (8) are the western Mississippi basin great plains; Arkansas, Missouri, Iowa, Oklahoma, Kansas, Nebraska, South Dakota and North Dakota, three (3) are on eastern tributaries of the Mississippi river; West Virginia, Kentucky and Tenessee and then there is Vermont.


Find your Hydrologic Unit Code (HUC)

Click to enter the USGS Locate your Watershed Page:

The United States is divided and sub-divided into successively smaller hydrologic units which are classified into four levels: regions, sub-regions, accounting units, and cataloging units. The hydrologic units are arranged or nested within each other, from the largest geographic area (regions) to the smallest geographic area (cataloging units). Each hydrologic unit is identified by a unique hydrologic unit code (HUC) consisting of two to eight digits based on the four levels of classification in the hydrologic unit system.

The second level of classification divides the 21 regions into 221 subregions. A subregion includes the area drained by a river system, a reach of a river and its tributaries in that reach, a closed basin(s), or a group of streams forming a coastal drainage area.The first level of classification divides the Nation into 21 major geographic areas, or regions. These geographic areas contain either the drainage area of a major river, such as the Missouri region, or the combined drainage areas of a series of rivers, such as the Texas-Gulf region, which includes a number of rivers draining into the Gulf of Mexico. Eighteen of the regions occupy the land area of the conterminous United States. Alaska constitues region 19, the Hawaii Islands are region 20, and Puerto Rico and other outlying Caribbean areas are region 21. [The regions are shown in figure 1.]

The third level of classification subdivides many of the subregions into accounting units. These 378 hydrologic accounting units are nested within, or can be equivalent to the subregions.

The fourth level of classification is the cataloging unit, the smallest element in the hierarchy of hydrologic units. A cataloging unit is a geographic area representing part of all of a surface drainage basin, a combination of drainage basins, or a distinct hydrologic feature. These units subdivide the subregions and accounting units into smaller areas. There are 2264 Cataloging Units in the Nation. Cataloging Units sometimes are called "watersheds".


EPA Watershed Tracking

Click to access the How's My Waterway application provided by the US Environmental Protection Agency to collect and deliver water quality information on individual watersheds.

USGS Stream Monitoring

Click to enter the United States Geological Survey (USGS) National Water Information System web interface to see realtime stream flow information.

Storm Drains

Storm drains flow directly to our rivers and streams unfiltered. Water is NOT diverted to a treatment facility. Storm drain water flows straight to a river or stream and eventually to the ocean. When it rains, anything dumped on the ground, roads, sidewalks, and driveways is washed into storm drains and water bodies. This includes pet feces, cigarette butts, trash, plastic bags and oil. Over 200 million gallons of used motor oil are improperly disposed of each year in America alone. That amount of oil is equal to about 19 Exxon Valdez oil spills.

The accumulation of pollutants leads to diminished water quality. Cigarette butts are the most littered item in America, and have been found in the stomachs of fish, birds, whales, and other marine creatures that mistake them for food. They contain thousands of chemicals that are carcinogenic to humans and the chemicals leach into water harming aquatic and marine life. Filters contain plastic, which breaks down but never disappears.

Dog waste is considered to be toxic by the EPA. The droppings Fido leaves behind contain disease-causing bacteria that can make people and wildlife sick. Dog waste can carry E.coli, fecal coliform, salmonellosis and other diseases. When it rains, dog waste is carried into storm drains and impacts creek and human health.

Washing your car can also have negative effects on our watersheds. If you wash your car in your driveway or a parking lot, the soapy water that washes off your car travels down the driveway and street and into the storm drain.

Dirty car wash water contains toxic pollutants from the car and the soap. Contrary to popular belief, this dirty wash water does not get cleaned at a wastewater treatment plant before it enters into the nearest stream, lake or sound. These contaminants can harm fish and wildlife, pollute streams, lakes and rivers, and even seep into our groundwater, an important source of drinking water.

Dead Zones

A dead zone is an area where nutrient levels are so high that the oxygen has been largely or entirely depleted. Marine life living in this zone either flee if mobile or die. One of the largest dead zones on the planet is the Gulf of Mexico where the mouth of the Mississippi—one of Colorado’s drainage point—ends.

The Gulf of Mexico supplies:

  • 72% of US shrimp
  • 66% of harvested oysters
  • 16% of commercial fishing

The impacts of dead zones can be devastating, both economically and environmentally. In Louisiana for example, the dead zone amounts to about 235,000 tons (470 million pounds) of seafood lost every year. Each year the size of dead zones shifts and grows. In 2015 it was nearly 6,500 square miles, roughly the size of Connecticut and Rhode Island combined. The dead zone ranges anywhere from 4,500-8,500 square miles of ocean.

Hypoxic zones can occur naturally, but they are greatly enhanced by human activity. Excess nutrients are the primary cause of dead zones. Nutrients lead to an overgrowth of algae, which eventually decomposes in rivers or the ocean, and oxygen is required to decompose the excess algae, depleting the surrounding water of the oxygen needed to support life. Marine life then either flee if able or are left to suffocate.

There over 550 dead zones worldwide, and the second largest resides in the northern Gulf of Mexico. In the United States, dead zones are also prominent on along the East Coast and in the Great Lakes.

Aligned Watershed Organizations