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Water Studies Precipitation and Population

The United States Geologic Survey provides the following information:

Rain - a Water resource

"In the United States, an average of some 70 percent of the annual precipitation returns to the atmosphere by evaporation from land and water surfaces and by transpiration from vegetation. The remaining 30 percent eventually reaches a stream, lake, or ocean, partly by overland runoff during and immediately after rain, and partly by a much slower route through the natural ground-water reservoir."

"Much of the rain that enters the ground, filters down into subsurface water-bearing rocks (aquifers) and eventually reaches lakes, streams, and rivers where these surface-water bodies intercept the aquifers. The portion of the precipitation that reaches the streams produces an average annual streamflow in the United States of approximately 1,200 billion gallons a day. By comparison, the Nations's homes, farms, and factories withdraw and use about 400 billion gallons a day."

The following table lists several major cities in the United States and the approximate amount of water each would receive in an evenly distributed inch of rain.

City Area*
Amounts of
(billions of gallons)
Average annual Precipitation

Est 2007

US Census Bureau

Gallons of water
per person
Atlanta, Georgia 86,976 2.36      
Boston, Massachusetts 29,440 0.80      
Chicago, Illinois 29,440 3.85      
Denver, Colorado 43,328 1.18      
Detroit, Michigan 88,320 2.39      
Los Angeles, California 291,264 7.91      
Miami, Florida 21,888 0.59      
Minneapolis, Minnesota 34,176 0.93      
New York, New York 191,808 5.21      
Philadelphia, Pennsylvania 82,240 2.23      
St. Louis, Missouri 39,168 1.06      
San Francisco, California 29,056 0.79      
Seattle, Washington 52,352 1.42      
Washington, D.C. 43,904 1.19      

*Areas within corporate limits of cities based upon Bureau of Census 1969 Statistics.

right pointing arrow Consider for a moment how much rainwater some cities may receive during a year.

"For example, Atlanta, Ga. averages about 45 inches of precipitation per year; multiplying this by the 2.36 billion gallons shown in the table as the number of gallons in 1 inch reveals that some 106 billion gallons of water fall on Atlanta in an average year. In a city the size of Atlanta, the per capita water use is about 110 gallons per day or 40,150 gallons per year. Thus, the water from a year's precipitation, if it could be collected and stored without evaporation loss, would supply the needs of about 2,640,000 people."

right pointing arrow Complete the table for each city. Use the most current data you can find.

right pointing arrow Evaluate: What does the data tell you?

Is there enough water for each person to use 100 gallons per day?

What factors impact having an adequate water supply?

What changes can be made to deal with a shortage of water?


Annual Climate Review U.S. Summary NOAA | Water Use at Home USGS Q&A | Water Use in the United States

right pointing arrow Challenge Question - How many baths can you get from a rainstorm?


Orme Tenn has run out of water

The Math of Sufficient Fresh Water video project

Lentic or Lotic Ecosystems online activity Water Study Index
Natural Resource Wars - who will be the winner? Wetlands EcoStudy Unit
Drought Presentation Learn About Watersheds activity
Water resources of the United States Great Lakes Commission
Water Vocabulary puzzle Great Lakes compact at the center of great debate
Make a Water crossword puzzle Water levels fall
Fresh Water facts activity Teaching with Data
Groundwater: A Primer for Pennsylvanians Southern States Fight for Water During Drought
What is a watershed? Watershed Atlas of the Allegheny and Monongahela Rivers
Protecting watersheds interactive guide Pathfinder Science - Stream Monitoring

"All of this avoidance of planning has been to avoid having to honestly state that there are limits to the amount of water available
in various parts of the state," said Neill Herring, an environmental lobbyist. "There are concrete limits to growth — and no one wants to admit that."

Useful links about water and the environment

This activity is aligned with the Pennsylvania State Academic Standards for Reading, Writing, Speaking; Environment and Ecology, Science and Technology, Mathematics, and Geography

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11/2007 Cindy O'Hora All Rights Reserved. FAQ Updated 12/2016
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