Your main water line is arguably the most important part of your home’s plumbing. It carries fresh water from the city’s supply into your home. It is located underground where it cannot be seen and can last up to 50 years when installed properly. If it fails, however, you may notice big problems like a drop in pressure or a higher water bill. Many factors impact the cost of a new water line, from how far the line has to travel to the diameter and material of the pipe..