blue water generally refers to water that can be delivered for irrigation or made available for alternative uses while green water must be used directly from the soil profile the terms green water and blue water generate easily recallable images of soil moisture and stored surface water in a manner that is likely to be helpful to many public officials and agency staff members some authors have suggested that the opportunity cost of green water is generally smaller than that of blue water they propose trading green water for blue water when possible to generate meaningful water savings