The answer to 'when to replace supply line' is that you should typically replace your plumbing supply lines every 5-10 years, or sooner if you notice any signs of wear or damage. Supply lines are the flexible hoses that connect your plumbing fixtures like sinks, toilets, and washing machines to the main water supply. Over time, they can become brittle, develop cracks, or start to leak, which can lead to water damage in your home.
It's a good idea to inspect your supply lines regularly and replace them proactively before they fail. Signs that it's time to replace a supply line include visible cracks, bulges, or discoloration, as well as any leaks or drips. Replacing supply lines is a relatively simple and inexpensive plumbing task that you can often do yourself, but it's best to call a professional plumber if you're not comfortable with DIY plumbing work.