Agriculture demands and consumes more water than any other economic sector and globally is responsible for more than 85 percent of all human-induced water withdrawals. The trend of increasing water scarcity across many countries will continue as gaps between water demand and supply are projected to widen due to factors such as economic growth, economic development, land degradation, and climate change. Within agriculture, many solutions are directed towards irrigated agriculture, as irrigation is the largest consumer of freshwater withdrawals in almost all water-scarce regions. However, a growing body of evidence shows that in many cases of expected water savings through improved irrigation technologies, there is actually an increase in water consumption. This publication is the starting point for using the Follow the Water (FtW) tool, which seeks to help users understand water flows in irrigation systems and detect the impacts of changes in irrigations systems’ allocations, consumptions and return flows. Users in education and training contexts, and in the initial design of irrigation systems can use the FtW tool to follow flows and the reuse of water in a simple and understandable manner.