The answer to 'why is my water line overflowing' is that there is a blockage or break in the main water supply line leading into your home. This can be caused by a buildup of debris, a tree root intrusion, or a crack or break in the pipe itself. Symptoms may include water pooling around the pipe, reduced water pressure, or water backing up into your home.
If the water line is overflowing, it's important to shut off the main water supply valve to your home as soon as possible to prevent further water damage. You'll then need to locate the source of the blockage or break and either clear the obstruction or have the pipe repaired by a professional plumber. Attempting to fix a major water line issue yourself can be dangerous and lead to further damage, so it's generally best to call in a licensed plumber for this type of repair.