The NPSI Knowledge Harvest brings together information from across the National Program for Sustainable Irrigation (NPSI) projects, highlighting key findings and promoting wider understanding. Key themes within the Harvest are: *Irrigation Overview - facts, figures and key concepts about irrigation. *Water Delivery Systems - the efficient storage and distribution of water for irrigation. *On-farm Irrigation Essentials - principles for efficient irrigation. *Recycled Water - recycling treated effluent and stormwater for irrigation. This document is part of the Irrigation Overview theme. It explores issues likely to affect the future of irrigation in northern and southern Australia, especially those related to ecology and natural environments, and provides tools for planners to address them.