A water trough (British terminology), or track pan (American terminology), is a device to enable a steam locomotive to replenish its water supply while in motion. It consists of a long trough filled with water, lying between the rails. When a steam locomotive passes over the trough, a water scoop can be lowered, and the speed of forward motion forces water into the scoop, up the scoop pipe and into the tanks or locomotive tender.
Origin
Steam locomotives consume a considerable amount of water, and the tender or side tanks need to be replenished at intervals. Traditionally the engine water was replenished during station stops, but if it was desired to run long distances without stopping, the requirement to take water was a significant limitation. The Railway Magazine reported a development by John Ramsbottom:
In the year 1860 the London and North-Western Company having decided to accelerate the Irish mail [express train], Mr. Ramsbottom, then their chief mechanical engineer, was asked to make the run between Chester and Holyhead, 84+3⁄4...