## Tuesday, February 7, 2012

### Water, Water Everywhere, Part II

Yesterday we looked at the percentage of water that makes up each of the states in the U.S. (See Water, Water Everywhere, Part I.) Today we'll see how our water use has changed as the population of the United States has grown.

Since 1950, the U.S. Geological Survey (USGS) has collected data on amounts of water used in homes, businesses, industries, and on farms throughout the United States. Water-use data are collected every five years. The USGS has compiled the data so we can see how our water use in the United States has changed over the past 50-plus years.
 San Diego River in California
In Excel Math, we teach children how to measure and compare data using tables and charts. Here's a chart from the 5th Grade Student Lesson sheets (see Section E) comparing the number of books read over three months by three different children:
And here's a chart from the U.S. Geographical Survey that shows the population growth and water usage in the United States since 1950. Between 1950 and 1980 there was a steady increase in water use. Contrary to what we would expect, reported water withdrawals in the United States declined in 1985 even though the population was still growing. Water withdrawals have remained relatively stable since then even though the population has steadily grown:
This chart shows the trends in surface-water and groundwater withdrawals for the United States from 1950 to 2005. We can tell that our Nation's water use peaked in 1980 and has been relatively steady since then.

Thanks to changes in technology, in State and Federal laws, in economic factors, and in water conservation, we are more efficient in our use of the water from the Nation's rivers, lakes, reservoirs, and aquifers. So even as the population grew, our use of water has become more efficient and our water consumption has remained relatively stable over the past 30 years.
 Old Mission Dam in California
Estimates of water use for the year 2000 indicate that about 408 billion gallons per day were withdrawn for all uses during the year. This total has varied less than 3 percent since 1985. Since then, withdrawals of water have stabilized for thermoelectric power and irrigation—the two largest uses.
 Cornfield in Iowa
Many of the stresses for greater water use have risen since 1980—population, the need to grow more food (irrigation), more industry, etc, but total water use has not risen. Water conservation and using water more efficiently have had a positive effect over the last 30 years.

From these charts, we can tell that more than one-fourth of the total water used in the United States in 2005 was withdrawn in California, Texas, Idaho, and Florida. California accounted for 11 percent of all withdrawals in the United States in 2005. Nearly three-fourths of the freshwater withdrawn in California was for irrigation, and 98 percent of saline water withdrawn was for thermoelectric-power generation.
 Thermoelectric power plant
Water withdrawals in Texas accounted for about 7 percent of the national total and were primarily for thermoelectric power and irrigation. Water withdrawals in Idaho were primarily for irrigation (85 percent) and aquaculture (13 percent). The water withdrawal figures for 2010 are still being compiled and won't be available until about 2014.

Until then, dive in...the water's waiting!
 Backyard swimming pool in California