During the era of steam railroading, the most essential occupation of railway operating departments was the provision of water and fuel at convenient locations and in continuous supply. Finding a sufficient and quality water supply for locomotive boilers was a particularly difficult problem. Operating conditions also presented problems to slower trains and those engaged in frequent stops or delays, resulting in the limited supply of water carried in the tender getting dangerously low or depleted entirely. This was partly overcome by building tenders of larger capacities but many of the older locomotives continued to use smaller tenders.
The spare water car soon became standard equipment in way freight and work train service. The tank was connected by suitable hose and valves to the tank well on the tender and the two tanks could be equalized or used independently.
Employees and their families living and working along the line often had no water supply, or else water was not drinkable. The spare water car was used to fill the cisterns which were placed at wayside locations. Track gangs often had one or more of these cars in their consist. Fresh cars would be delivered to them as needed and the empties returned for refilling.
Many ingenious methods were developed to prevent freezing in winter conditions. One was a good pail of 'dope': wool waste saturated with car oil and used for packing journal boxes. The 'dope' was placed at the problem area and set alight. It was a sight to behold: a water car, tender pipe and locomotive feed pipe all ablaze as crews or shop employees fought to thaw out the equipment.