Contaminated drinking water

Earth’s Water

What is the water cycle? I can easily answer that—it is “me” all over! The water cycle describes the existence and movement of water on, in, and above the Earth. Earth’s water is always in movement and is always changing states, from liquid to vapor to ice and back again. The water cycle has been working for billions of years and all life on Earth depends on it continuing to work; the Earth would be a pretty stale place without it.

Where does all the Earth’s water come from? Primordial Earth was an incandescent globe made of magma, but all magmas contain water. Water set free by magma began to cool down the Earth’s atmosphere, and eventually the environment became cool enough so water could stay on the surface as a liquid. Volcanic activity kept and still keeps introducing water into the atmosphere, thus increasing the surface- and groundwater volume of the Earth.

A quick summary of the water cycle

Here is a quick summary of the water cycle. The links in this paragraph go to the detailed Web pages in our Web site for each topic. A shorter summary of each topic can be found further down in this page.

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.”

Main components of the water cycle

Helpful information and material to assist you with water education.

This information can assist you in developing and administering your own water quality programs that help protect health, and quality of life.

Water Education Sites that contain lesson plans or projects.

Information aimed at educators.

AQUATOX
Learn about AQUATOX, a program that models how nutrients and pollutants affect freshwater ecosystems, by viewing slides from the last AQUATOX training session.

BASINS
BASINS is a multi-purpose environmental analysis system that integrates a geographical information system (GIS), national watershed data, and state-of-the-art environmental assessment and modeling tools into one convenient package.

Clean Water Act Section 404 Regulatory Training
This four-day course provides an introduction to the Clean Water Act Section 404 regulatory program and training in the application of the 404(b)(1) guidelines for review of proposed discharges of fill material into waters of the United States.

Drinking Water Academy
The Drinking Water Academy provides information and online training modules to ensure that water professionals, public officials, and involved citizens have the knowledge and skills necessary to protect our drinking water supply.

Drinking Water Operator Certification
Operator certification helps protect human health and the environment by establishing minimum professional standards for the operation and maintenance of public water systems. A compilation of training materials, tools and guidance to help operators become and remain certified is available.

Long Term 2 Enhanced Surface Water Treatment Rule Training
If you are implementing the Long Term 2 Enhanced Surface Water Treatment Rule (LT2) you may use our on-line module or request a Webcast for training. New Webcasts and other training opportunities will be posted.

NPDES Training Courses and Workshops
The National Pollution Discharge Elimination System (NPDES) permitting program offers training courses, workshops, and webcasts to explain the regulatory framework and technical considerations of the NPDES permit program. These courses are designed for permit writers, dischargers, EPA officials, and other interested parties.

Water Quality Standards Academy
To support water quality standards development, we offer the Water Quality Standards Academy (WQSA), which presents classroom-based and online courses, along with occasional webcasts.

Tribal Training
This site contains a consolidated, centralized listing of training courses offered by EPA that will help Indian tribes develop and implement water quality programs consistent with the Clean Water Act. It will enable Indian tribes to obtain, in one central place, a list of relevant training courses consistent with the goals established for individual reservations.

Watershed Academy
The Watershed Academy is a focal point in EPA’s Office of Water for providing training and information on implementing watershed approaches.

Wastewater Operator Training
The Clean Water Act authorizes funding for the Wastewater Treatment Plant Operator On-Site Assistance Training Program. The program addresses non-compliance at small publicly-owned wastewater treatment plants and ensures enough trained personnel are available to operate and maintain existing and future treatment works.