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 in the plumbing system. The symptoms may include water leaking or spraying from the burst pipe, low water pressure, or water damage to the surrounding area. To fix a burst supply line, you'll need to turn off the water, drain the system, and replace the damaged section of pipe.
If the burst pipe is easily accessible and the damage is minor, you may be able to fix it yourself by cutting out the damaged section and replacing it with a new length of pipe and fittings. However, if the damage is extensive or the burst pipe is in a difficult-to-reach area, it's best to call a professional plumber to handle the repair. They have the tools and expertise to safely and effectively fix the problem.