Without one, or any type of water storage device a locomotive's range was limited, usually 10 miles or less since water was consumed at a far higher rate than heating fuel (early on this consisted of coal/wood and then later oil was used). In addition to producing steam, the ultimate source of a locomotive's power, water was extremely important to the boiler's well-being. It must remain high enough to cover the firebox or the resulting heat could cause a failure of the entire system and explode. Despite their romance steam locomotives, and any type of equipment employing a boiler, are dangerous machines. Water levels must be constantly monitored (in the old days engineers relied on a sight glass in the cab) and the shell must be strong enough to support the required steam pressure.
According to one expert a general rule of thumb pertaining to a steam locomotive's water consumption is as follows (again, these numbers are general as obtaining correct figures is specific for each individual steam locomotive requiring precise equations relating to BTU's per minute divided by the fuel being used [among other calculations, as the locomotive's drawbar horsepower is also needed to achieve correct figures]:
During light working conditions, 18,000 pounds of water are available per every ton of coal consumed.
In moderate working conditions, 13,000 pounds of water are available for every ton of coal burned.
Finally, with heavy working conditions, 11,000 pounds of water are available for every ton of coal consumed.
These numbers were derived using post-20th century, modern locomotive designs. What began as such a simple device became a highly advanced machine by the 1940s. The tender could greatly extend a locomotive's range and by the late steam era (1930s-1940s) a locomotive used in main line service could run anywhere between 75 to 150 miles before needing to refuel, which typically coincided with a train crew's district/territory. This distance was also how far most railroads placed maintenance terminals/facilities since steamers needed constant care whether it be lubrication, fuel, sand, or some other requirement. Of course, liquid H2O was always the most precious commodity; railroads typically placed at least one water tank, plug (similar to a tank but without a storage device and only tall enough to fit over the tender with a discharge chute which pumped water), or "tank pond" (located near the tracks they were fabricated by damming nearby creeks or streams) half-way between terminals as a safety precaution.
The water tank became a bucolic object during the romantic era of railroading when trains were the only way to travel and steam locomotives were commonplace. It could be found in the smallest of towns, awaiting its next tenant, while in some cases stops were placed miles from the nearest home. Alas, with the invention of the diesel locomotive water tanks disappeared in the post World War II era; diesels, which required far less fuel and maintenance, enabled railroads to push districts and maintenance facilities much further apart. Additionally, there was no need for watering stops since there was no need for water. Today, these relics from the past can still be found decaying along a few rights-of-way while others have been restored. In some cases, original examples are still used as they were intended, such as on the Cass Scenic Railroad and Durango & Silverton Narrow-Gauge.
Glossary And Terms
The Water Tank