Part 5 of a series about basic water law in the United States, predominately in the western part of the country, and how it affects this finite resource. Water law can be traced back to Roman times and also has roots in English common law. Across the United States, it varies from state to state, and from East to West. When conflicts arise, courts usually determine the outcome, unless there are state or federal laws or previous case studies to resolve the issue. Exceptions to the law can arise from differences in each state’s water laws.