As previously stated, the relation between the boiling point of water (which also is the generating point of steam) and pressure is absolute. Under a given pressure water will boil and steam will generate at a certain temperature. Increase the pressure and the point at which the water will boil will also increase. Thus, at atmospheric pressure, water will boil at 212 degrees Fahr., while if the pressure is increased 50 pounds, a common pressure for water in city mains, the boiling point of the water will be increased to 297 degrees Fahr.

If water under pressure is raised to a temperature above 212 degrees Fahr. and then released to the atmosphere, part of the water will instantly flash into steam and continue to generate steam until the temperature of the water is reduced below the boiling point at atmospheric pressure. Thus when water under pressure in a tank is raised to the boiling point at that pressure and a hot water faucet is opened, steam will flow from the faucet with a sputtering sound caused by the mixture of water with the steam. This flow of steam will continue until the temperature of the water in the tank has been lowered by the inflowing cold water to below 212 degrees Fahr. The hot water tank is not full of steam, as would appear to the person at the faucet, but the water is instantly converted into steam as soon as the pressure is released from the water at the faucet. The overheating of water in a tank can be prevented by the use of temperature regulators, which are made to control the supply of steam to steam coil, also to regulate the drafts to water heaters, and by these means maintain a uniform temperature of water in a tank.