Agriculture is one of the most insatiable consumers of dwindling water resources around the world. And food production will need to increase by about 70% over the next 35 years to meet the needs of a growing population. Crops aren't creating the only demands; agriculture will face competition for water from cities, industries, and recreation.

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?

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 The reuse of gray water for agriculture can decrease the amount of blue water withdrawn from stores and increase the green water available for plants to use.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."