Customers 40 gallon water heater was leaking from bottom. Tank was original to home approximately 20 years old. Shut water off to tank and removed original tank. Provided and installed new 40 gallon Bradford White natural gas atmospheric water heater to code. Turned water back on to tank and bled air from system. Had customer bleed air from taps inside home. Tested for leaks on both gas and water supplies. Lit tank and set temperature to hot position. Informed customer on how to set higher and lower temperatures on valve and how to relight pilot. Disposed of old tank.