Need more tongue weight. Will a water tank up front do?

If that is a 5th wheel style trailer frame you need about 3000 pounds on the pin. If it is a bumper pull style trailer you still need close to 2000 pounds on the tongue. Unless you mount that tank right on the tongue you will not get there that way. 1000 pounds mounted 2 feet ahead of the axles probably only adds 150 pounds to the tongue so placing it as far forward as possible is crucial.

Easier to move axles.