Your water meter is typically found in the front yard, near the street or sidewalk. The water service line will be the pipe connected to the water meter that comes into your home from the street.
The water service line will enter your building in the closest location to the meter (basement, crawl space, front closet, etc.) and will be visible with a shutoff valve. It is typically located in a utility room on the lowest level of your home and may be accessible in a crawl space if your home has one.
For this effort, we are only interested in the service line material up to the shutoff valve, not beyond, and this is typically the first 18 inches of pipe coming through the floor or exposed in the crawl space. We do not need to know the material of the plumbing in your home or business. Note that usually your water service line is not the pipe located under your kitchen sink.