Q: Water leak, don't know where

If your engine has no external coolant leaks, and is still requiring you to put water in the radiator, that water is leaking internally inside the engine. But before jumping to that conclusion, a cooling system pressure test should be performed. Pressuring the cap and entire cooling system will indicate any leaks. The system should also be filled with a 50/50 mixture of coolant and distilled water. If plain water is used it boils at too low a temperature and may be boiling over under normal temperatures causing loss of water (especially if radiator cap is bad). Internal leakage into the engine can happen when a cylinder head gasket fails. It’s also possible leakage from an intake manifold gasket, or a cracked head. A technician from YourMechanic can diagnose your car for leaks at your home or office. Upon repair, you will be reimbursed any inspection fees.