[l2ridehd]

There are a few possibilities.
1. First verify that nothing else is attached to the fuse box. The dryer maybe?

2. If the fuse box is really dedicated to the water heater only and the breaker in the electric panel is dedicated to the water heater only and is also 30 amp, the old screw panel can be eliminated.

Perhaps when the breaker panel was installed and eliminated an older fuse panel the wire run for the water heater was run only to the fuse panel. At one point many years ago, some electric companies used to have two meters on homes with one dedicated to hot water which was a lower rate. That may be why there is a 30 amp 220 fuse box next to the water heater.

Now if anything else is connected to the fuse panel or the breaker, I would split that off and install to a new breaker. Then also eliminate the fuse panel. The circuit you describe with a 30 amp breaker feeding a 30 amp fuse panel has no value and is a bit of a hazard. If possible you may want to replace the wire from the fuse panel to the water heater with a new 10-3 romex line.

If you have any electrical experience at all, you can do this. It is really fairly straight forward. Just make sure breaker is off and using a very simply tester that no power is present any where your working.