Importance of return flow as a component of water use

Understanding the relation between the hydrologjc cycle and water use is important for effective water-resources management. The hydrologic cycle is the natural pathway of water from evaporation to precipitation to infiltration or runoff and to storage from which evaporation can again occur. The science of water use is the study of human influences on the hydrologic cycle. Human activities affect the hydrologic cycle by changing the quantity, distribution, and quality of available water. Quantifying return flow is useful to water managers in evaluating such changes. Return flow is often thought of as what runs down the drain, or what is leftover after the water's purpose has been served. As innocuous as that may sound, return flow plays a significant part in the overall water-use picture.