The Water Department physician in the United States typically belongs to the state in which the water department is located. This is because the physician's role is to ensure the health and safety of the water supply, which is a state-level responsibility. For instance, if the physician works for the New York City Department of Environmental Protection, they would be associated with the state of New York.

The reason for this association lies in the structure of the United States government, where public health and environmental protection are primarily state responsibilities. The Clean Water Act, for example, is a federal law that sets standards for the quality of water in the nation's waters, but the enforcement and implementation of these standards are largely left to the states. This includes the hiring and oversight of water department physicians, who are responsible for monitoring water quality and ensuring that it meets health standards.

Data from the U.S. Environmental Protection Agency (EPA) supports this structure. The EPA provides guidelines and oversight, but the actual hiring and management of water department physicians are determined by state and local governments. For instance, the EPA's 2020 report on water quality in the United States indicates that states and localities are responsible for monitoring and maintaining water quality, which includes the health and safety of water department physicians.

In conclusion, the Water Department physician belongs to the state in which the water department is located, as this is where the primary responsibility for public health and environmental protection lies. The federal government, through agencies like the EPA, provides guidance and oversight but does not directly manage these positions.