Throughout human history various laws and customs have developed concerning the individual rights and rights in common to the waters of the earth. Many existing laws and concepts are clearly influenced by the environment in which they originated and reflect the relative abundance or scarcity of water. Many concepts reflect the people's original interests in the water and once established have been passed from generation to generation with little modification. Some laws and concepts have been carried by people in their migrations and colonial expansions to vastly different environments, with rather curious consequences. In many places water laws that had been well adapted to the natural environment have become less tenable because of man's activities in modifying that environment, or because of increasing use of water: Increasing consumptive use shifts the water economy toward lesser abundance or increasing deficiency; increasing nonconsumptive use results in pollution of the water resources, so that they become less suitable for other users. The water-rights systems in the United States vary from State to State: some are reasonably fitted to their environment, some have outlived their place in history, some are wasteful of water, some show favoritism to certain special interests or segments of the population. Water-use rights are universally recognized as real property, with constitutional protection against deprivation without due process of law.