Water law in the United States

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Water law in the United States refers to the Water resources law laws regulating water as a resource in the United States. Beyond issues common to all jurisdictions attempting to regulate water's uses, water law in the United States must contend with:

• Public regulation of waters, including flood control, environmental regulation—state and federal, public health regulation and regulation of fisheries
• The interplay of public and private rights in water, which draws on aspects of eminent domain law and the federal commerce clause powers;
• Water project law: the highly developed law regarding the formation, operation, and finance of public and quasi-public entities which operate local public works of flood control, navigation control, irrigation, and avoidance of environmental degradation; and
• Treaty rights of Native Americans.

The law governing these topics derives from all layers of US law. Some derives from common law principles which have developed over centuries, and which evolve as the nature of disputes presented to courts change. For example, the judicial approach to landowner rights to divert surface waters has changed significantly in the last century as public attitudes about land and water have evolved. Some derives from state statutory law. Some derives from the original public grants of land to the states and from the documents of their origination. Some derives from state, federal, and local regulation of waters through zoning, public health, and other regulation. (Federally recognized tribes may have water rights, but non-federally recognized Indian tribes generally do not.)