Scientists have few categories at their disposal to describe droughts, which are more complex than mere shortages of precipitation or surface water. For example, some local shortages can be invisible, as when water is transferred into a dry area from a distant source. Other shortages are chronic, with communities continuously requiring more water than is available, even in wet years. Some water shortages occur when water quality becomes so degraded that even though there may be plenty of water available, little of it is usable. With such variation in conditions, scientists need better language to conceptualize droughts.