This article deals with legal challenges in conserving water in the United States, using Kansas as an example. The focus is on one aspect of American water allocation law—the extent to which a state can force reductions in pumping by holders of water rights. It explains the hybrid nature of water rights, which on the one hand are “real property rights,” and yet on the other hand they are viewed as rights only to use water and not to own the water itself. Because they are a kind of property right, they are protected by the fifth amendment to the U.S. Constitution against “takings” by the government without compensation. The question becomes: to what extent, then, can states demand reductions in pumping without having to pay compensation? The answer is difficult for both water right holders and government officials to predict. The law of groundwater rights in Kansas illustrates the problem. The article describes the Kansas law in the context of other states on this issue, including the historic changes in Kansas’ water law doctrines, water management under the appropriation doctrine, the public trust doctrine, groundwater management districts, and intensive groundwater use control areas, as well as recent attempts to foster voluntary actions by water right holders that avoid government imposition of restrictions. Questions remain in Kansas and elsewhere about where the line can be drawn, between acceptable government restrictions and unacceptable takings of property. Future drought caused by climate change will focus even more attention on this question