We often take water for granted. The human body is about 70% water and 75% of the Earth’s surface is covered by water—but less than 1% of this supply of water is potable (drinkable).

“Water, water, everywhere, but not a drop to drink!” The water supply is finite and we need to use water wisely.

I recently read Rainwater Harvesting for Drylands Vol. 1, by Brad Lancaster (Rainsource Press, Tucson AZ, 2006; www.HarvestingRainwater.com). Although this book was written for areas like Arizona, New Mexico, or Texas, the principles of saving water will apply anywhere.

Since we know that the supply of water is finite, and states are already fighting legal battles for water rights for transportation as well as drinking water—so paying for large quantities of water will become expensive in the future—we should do everything we can to wisely manage the water that falls on our land. On a typical farm, agriculture uses 70% of its water, so saving and managing any water you get is prudent—and reduces topsoil loss.

The area I live in (Clark, Missouri) is blessed with bountiful rain—32-48 inches per year. To give you an idea of what that means, Brad Lancaster provides a handy formula on how to calculate rainfall volume (gallons per year): Take the square feet of land (or of an area such as a roof) times the rainfall in feet (the average in Missouri is 40 inches, or 3.33 feet) times 7.48 gallons of water per cubic foot.

So, 43,560 sq. ft. (1 acre) x 3.33 feet in rainfall x 7.48 gal./ft.3 = 1,085,010 gallons/acre/year. That means my 80-acre farm receives almost 87 million gallons per year.

Rainwater Harvesting for Drylands Vol. 1 gives the following average coefficients for water runoff: roof or solid paving—0.80-0.95 (80-95% of the water runs off and is lost, the rest evaporates or is absorbed; a lot of water comes off roofs that could be stored); bare earth—0.35-0.55; grass/lawn—0.10-0.25. Grass obviously has the least runoff—but poor pasture or bare earth can lose up to half of the water falling on it! Managing water is important.

Corn is an efficient user of water for the pounds of dry matter it produces, but it still takes 5,000 gallons of water to produce 1 bushel of corn. Modern Corn Production, Second Edition, by Samuel Aldrich, Walter Scott, and Earl Leng (A&L Publications, Champaign IL, 1975) states that in the Corn Belt, we seldom get enough rainfall during the growing season (April 1-September 30). It takes 18-24 inches to produce 100-175 bushels of corn. If it does not come from rainfall, it must come from expensive irrigation or the subsoil—which recharges from roughly September of one year to May of the next. From May 15 to August 31, the crop depends on subsoil moisture and rainfall.

It is easy to see how necessary the water reserve is to the growing crop cycle, and we must do the right things at the right time in the cycle, so water will be available for the growing crop.

Slowing water runoff on your farm reduces erosion and allows you to store water in the subsoil for future use. Think about your water use for 2009 and how to improve it—it will pay great dividends.