Technician arrived to a water heater that was leaking inside of the jacket very bad. Explain to customer that the tank need to be replaced immediately and the hazards that were in place. Customer agreed authorize work to be performed well tank was drain down cut out and a new Bradford white similar 40 gallon natural gas tank was installed, with an upgrade to the exhaust flue. Tank was filled and fired and seems to be functioning properly at this time without any leaks or issues.