The answer to 'why is my supply line burst pipe' is that a burst supply line is usually caused by high water pressure, freezing temperatures, or corrosion. The supply line is the pipe that carries water from the main shut-off valve to your plumbing fixtures, and it can rupture or burst due to these common issues. Symptoms include a sudden loss of water pressure, water leaking around the supply line, or water pooling on the floor.
If you have a burst supply line, the first step is to turn off the main water shut-off valve to stop the leak. Then you'll need to replace the damaged section of pipe. This may be a simple DIY repair if the issue is localized, but if the problem is more extensive or you're not comfortable making the repair, it's best to call a professional plumber.