Years ago in Tacoma, city water made the final hookup to a new sub division of high end houses. They had just finished when a guy came up and asked them what they were doing with his pipe. They said who are you? He replied he was the sewer dept supervisor and that the water main was 4 feet deeper. Yup, they hooked an entire new subdivisions water system to a high pressure sewer line. Water dept spent the next month flushing and chlorinating the system.