Anyone who makes their own meals knows how easy it is to boil the kettle or saucepan dry. You can't allow that to happen with a steam locomotive, yet the same principles are in force. In fact, it's rather more precarious because, in a locomotive, the boiler is managed so that it produces a constant amount of steam at its maximum limitations, yet it must never be allowed to ‘boil dry.’
With the supply of water available from tender or tanks limited by their capacity, it would be necessary, on longer journeys, to stop and top up with water from a lineside supply. Accordingly, stations large and small were provided with water columns and, where necessary, water storage tanks to supply them. On the Midland main line, where slow coal…