The term "First Water" actually dates back to the 1800's when fire departments actually competed with one another.

When two departments were in the same area, the town would often only pay the first fire department on scene, while the second received nothing. In other areas it was a matter of pride.

The first department to put water on the fire would claim "First Water" and, in a way, get credit for fighting that fire. Some departments even hired young kids who would race to a fire on foot and throw a single bucket of water on the flames. This usually did very little or nothing to fight the fire, but it would earn that department the right to claim "First Water".