Pour water on fuel rail to start

Truck starts great when cold but won't start sometimes after driving around town. The motors spins over but it's not getting fuel or fire. Somebody told my Dad to pour water on what looks like a fuel rail going to the injectors to "reset" something. It works! The truck will immediately start after doing this. Any ideas on what is "resetting"? What needs replacing in case I get caught out without any water?

 

In the old days the fuel system would get vaporlock and pouring cool water on the lines/filter etc. would condense the vapor back to a liquid and fix the no start problem.

 

Interesting, didn't know this. thank you