Water trucks I have seen do not have a gallon meter on them. They are not selling you water by the gallon like a fuel truck. They sell you a load which is more or less the capacity of the tank.Hi Dirk, I'm jumping onto this thread because your response brought a question to mind. If my new pool is going to be filled from a water truck, will the truck operator be able to tell exactly the volume of water needed to fill my pool? I'm guessing this is something I should try to remember to ask when the time comes.