Improving water security with blue, green, and gray water

With limited water and the increasing number of people depending on it, water security is tenuous. But integrated water management plans using "blue," "green," and "gray" water can increase water security. What do these colors mean and why are these waters vital?

Those are the central questions behind the symposium "Blue Waves, Green Dreams, and Shades of Gray: Perspectives On Water" being held Nov. 5. The symposium is part of the American Society of Agronomy, Crop Science Society of America, and the Soil Science Society of America Annual Meetings, Nov. 3-6 in Tampa, Florida.

Blue water is found in lakes, rivers, reservoirs, or aquifers. It is used for many purposes such as drinking water, water for homes and businesses, and irrigation water for agriculture. Freshwater stores are limited, and what's left of blue water must be protected and used sparingly.

Green water is the water available in the soil for plants and soil microorganisms. It can be absorbed by roots, used by the plants to grow, and released back to the atmosphere. The use of green water by crops must be optimized to better utilize this often overlooked resource.

Gray water is water that has been previously used and may contain some impurities. It can come from cities, households, or industries, and it is waste water that is usually treated and discharged. The reuse of gray water for agriculture can decrease the amount of blue water withdrawn from stores and increase the green water available for plants to use.

These three water sources -- blue, gray, and green -- have to be protected and optimized if agriculture is to rise to the challenge of feeding over 9 billion people by 2050 while leaving enough water for other uses. After all, says Rattan Lal, presider of the symposium, "There is no substitute for water."