Abstract: Hydrogen leakage from a generator core through stator windings into the generator coolant water is measured by flowing air into the coolant water exiting the stator windings and measuring the hydrogen content of the gas vented from a coolant water reservoir. The flow of air into the coolant water also oxygenates the coolant water to prevent undesirable formation of less stable cuprous oxide layers and enhance the formation of a protective cupric oxide film on the inside surfaces of the copper stator windings. In another form, trace gas is introduced into one of the generator core environment and the coolant water and a detector measures the magnitude of the trace gas leaked between the generator core environment and the coolant water as an indication of the magnitude of hydrogen leakage escaping from the generator core into the stator water coolant system.