Abstract: A valve assembly is operative for automatically shutting off both a water supply line and gas supply line to a gas-fired hot water vessel upon detection of water discharge, leak or overflow, from the water vessel. The valve assembly is connected in the water supply line and generally includes a valve body, a sliding valve member which is spring biased to a normally closed position, and a water softenable latch which maintains the valve member in an open position against the bias of the spring. The valve assembly is preferably positioned in a drip pan located under the water vessel such that water leaking from the water vessel will accumulate in the drip pan and submerge the valve assembly. Upon exposure to water accumulated in the drip pan, the water softenable latch at least partially softens and releases the valve member to move from its open position to its closed position to cut off water supply through the valve body.