To achieve a leak-free plumbing system, ensure that fittings are securely installed and compatible with the pipes they connect to. Use appropriate sealing materials, such as Teflon tape or pipe thread sealant, when connecting threaded fittings. For compression fittings, tighten them to the manufacturer's recommended torque. Additionally, conduct regular inspections and maintenance to identify and address any potential leaks early on, preventing larger issues down the line.