The impact of human activities and structures on the water cycle are discussed. Return to Basics Menu Nature recycles the earth's water supply through a process known as the water cycle or hydrologic cycle . This cycle operates continuously and receives energy from the sun. The hydrologic cycle consists of inflows, outflows, and storage. Inflows add water to the different parts of the hydrologic system, while outflows remove water.
Storage is the retention of water by parts of the system.
Because water movement is cyclical, an inflow for one part of the system is an outflow for another. Looking at an aquifer as an example, percolation of water into the ground is an inflow to the aquifer. Over time, if inflows to the aquifer are greater than its outflows, the amount of water stored in the aquifer will increase. Conversely, if the inflows to the aquifer are less than the outflows, the amount of water stored decreases. Inflows and outflows can occur naturally or result from human activity.