The answer to 'what causes supply line' is that a supply line can become damaged or clogged for a few common reasons. Supply lines are the flexible hoses that connect your plumbing fixtures like sinks, toilets, and appliances to the main water supply. Over time, these lines can develop cracks, holes, or mineral buildup that restricts water flow.
Some of the most common causes of supply line issues include high water pressure, corrosion from hard water, physical damage from bumps or wear, and old age. When a supply line fails, it can lead to leaks, low water pressure, and even water damage in your home.