St. Tammany Water Works v. New Orleans Water Works was a United States Supreme Court case that addressed the issue of whether a state could grant a private corporation the exclusive right to supply water to a city. The case was brought by St. Tammany Water Works, a private corporation, against New Orleans Water Works, a public corporation. The Supreme Court held that the state of Louisiana had the power to grant exclusive rights to a private corporation to supply water to a city. The Court reasoned that the state had the power to grant exclusive rights to a private corporation because it was in the public interest to do so. The Court also held that the state had the power to regulate the rates charged by the private corporation. The Court's decision in this case established that states have the power to grant exclusive rights to private corporations to supply water to cities. This decision has been cited in numerous cases since then, and it has been used to support the idea that states have the power to grant exclusive rights to private corporations to supply other services, such as electricity and telecommunications.

In St. Tammany Water Works v. New Orleans Water Works, the Supreme Court was tasked with determining whether a state law that allowed for the construction of a waterworks system in one parish (St. Tammany) could be applied to another parish (New Orleans). The majority opinion held that it could not, as this would violate the contract clause of the U.S Constitution which prohibits states from passing laws impairing contracts between private parties without just compensation being provided to those affected by such laws. Justice Field dissented from this ruling and argued that while he agreed with much of what was stated in the majority opinion, he felt there were certain aspects of Louisiana's civil code which should have been taken into consideration when making their decision on this case; namely Article 745 which allows for public works projects to be constructed across multiple parishes if they are deemed necessary or beneficial for public health and safety reasons - something both sides had agreed upon here given how important access to clean drinking water is considered today. He further noted that any potential harm caused by allowing such an action would likely be minimal compared to its overall benefit so long as proper safeguards were put in place during construction and operation phases alike; thus concluding his dissent by stating his belief that it should have been left up to local authorities rather than federal courts alone when deciding whether or not such actions should take place within their respective jurisdictions going forward