Water law

Water law is the field of law dealing with the ownership, control, and use of water as a resource. It is most closely related to property law, but has also become influenced by environmental law. Because water is vital to living things and to a variety of economic activities, laws attempting to govern it have far-reaching effects.

Water has unique features that make it difficult to regulate using laws designed mainly for land. Water is mobile, its supply varies by year and season as well as location, and it can be used simultaneously by many users. As with property (land) law, water rights can be described as a "bundle of sticks" containing multiple, separable activities that can have varying levels of regulation. For instance, some uses of water divert it from its natural course but return most or all of it (eg. hydroelectric plants), while others consume much of what they take (especially agriculture), and still others use water without diverting it at all (eg. boating). Each type of activity has its own needs and can in theory be regulated separately. There are several types of conflict likely to arise: absolute shortages; shortages in a particular time or place; diversions of water that reduce the flow available to others; pollutants or other changes (such as temperature or turbidity) that render water unfit for others' use; and the need to maintain "in-stream flows" of water to protect the natural ecosystem.

One theory of history, put forward in the influential book Oriental Despotism, holds that many empires were organized around a central authority that controlled a population through monopolizing the water supply. Such a hydraulic empire creates the potential for despotism, and serves as a cautionary tale for designing water regulations.

Water law involves controversy in some parts of the world where a growing population faces increasing competition over a limited natural supply. Disputes over rivers, lakes and underground aquifers cross national borders. Although water law is still regulated mainly by individual countries, there are international sets of proposed rules such as the Helsinki Rules on the Uses of the Waters of International Rivers and the Hague Declaration on Water Security in the 21st Century.

Long-term issues in water law include the possible effects of global warming on rainfall patterns and evaporation; the availability and cost of desalination technology; the control of pollution, and the growth of aquaculture.