In one bathroom the tap water smells like sewage, but not in the other bathroom or the kitchen. What could cause this? Once I run the water for 30 seconds the smell disappears. Duplex is 18 years old and on city water.

Sounds like you picked up some bacteria in your tap. Shut the water off to the tap, and opened up. Pull the cartridge and aerator and soak them in bleach. Also fill the open valve body with bleach and let it set a while. Reassemble and test. Smell better now? Good luck, Tom

Are you sure the odor is in the tap water, most public water supply systems use chlorine to sanitize the water. Sometimes organic matter ( hair, skin, syliva, etc. ) can accumulate in the sink basin overflow port and corresponding drain pop - up assembly cavity. This material can fester and create an offensive odor...