The answer to 'my water line replacement smells bad' is that a foul odor coming from a new water line is often caused by bacterial growth or chemical reactions within the pipes. This can happen when the new pipes are not properly flushed and disinfected before use.
Some common symptoms include a rotten egg or sewage-like smell coming from faucets and fixtures. This is typically due to the presence of sulfur-producing bacteria that thrive in stagnant water. In some cases, the smell may also be caused by chemical reactions between the new pipes and the water, which can produce unpleasant odors.