The answer to 'why is my supply line overflowing' is that a supply line overflow is typically caused by a blockage or leak in the line. This can happen when the supply line becomes clogged with debris, mineral buildup, or other obstructions, preventing the water from flowing properly. It can also occur if there is a crack or hole in the supply line, allowing water to leak out and back up into the line.
Some common symptoms of a supply line overflow include water pooling around the appliance or fixture, a slow draining or non-functioning fixture, and potentially water damage to the surrounding area. To address the issue, you'll first need to identify the source of the problem, which may require inspecting the supply line or calling in a professional plumber.