There are many places a water main can be found inside a house. It almost certainly is along the perimeter of the house and near ground level. It is likely to be in close to a straight line from the water meter and behind an access panel.
The location of a water main shut off can be difficult to find. It is best to find the shut-off valve before an emergency requires it to be shut off quickly. Walls that do not border the outdoors should not be searched, unless all other options have been exhausted.
The shut-off will also be relatively even with the ground outside of the house. That means that it will be found at eye level or above in a basement or at floor level on a ground floor.
Making a mental line from the outside water meter to the interior of the house can be useful if the shut-off is difficult to find. The shut-off may be behind an access panel because it is not supposed to be behind an insulated wall. It is important to know that the shut-off will most likely not be underneath any sink or connected to the toilet, washer or water heater. Information on where the shut-off valve is may be found in section 6.1 of the home inspection report.
Once the shut-off valve has been found, it must be turned clockwise until it stops moving.