Water resources law (in some jurisdictions, shortened to "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, and is distinct from laws governing water quality.
Water is ubiquitous and does not respect political boundaries. Water resources laws may apply to any portion of the hydrosphere over which claims may be made to appropriate or maintain the water to serve some purpose. Such waters include, but are not limited to:
Surface waters—lakes, rivers, streams, oceans, and wetlands;
Surface runoff—generally water that flows across the land from rain, floodwaters, and snowmelt before those waters reach watercourses, lakes, wetlands, or oceans;
Groundwater—particularly water present in aquifers.
The history of people's relation to water illustrates varied approaches to the management of water resources. "Lipit Ishtar and Ur Nammu both contain water provisions, pre-date Hammurabi by at least 250 years, and clearly provide the normative underpinnings on which the Hammurabi Code was constructed." The Code of Hammurabi was one of the earliest written laws to deal with water issues, and this code included the administration of water use. At the time the code was written in ancient Mesopotamia, the civilizations in the surrounding lands were dependent on the Tigris and Euphrates rivers to survive. As a result, the leaders needed to develop intricate canal and irrigation systems to sustain their needs for the water. The code was developed about 3,800 years ago by King Hammurabi of Babylonia.
Water is uniquely difficult to regulate, because laws are designed mainly for land. Water is mobile, its supply varies by year, season, and location, and it can be used simultaneously by many entities. As with property 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 (e.