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 residual debris in the pipe. This can happen when the water line is not properly flushed and disinfected during the replacement process.
The most common symptoms are a rotten egg or sewage-like smell coming from your faucets or fixtures. This is usually not a health hazard, but it can be very unpleasant. To solve the problem, you'll need to thoroughly flush and disinfect the new water line.