Just pull the blower fuse when it is not actually in use. You do not need an amp draw meter yet in my opinion. Although you might want to periodically measure the battery voltage with the engine running.

It might be there but too low to keep up with needs. Your looking for at least 13.5 volts at idle. Forget water splashing on the alternator as the direct cause. Almost all cars experience this with no issues generally.

There is also a possibility of confusion here. Can you reach down and turn the alternator pulley by the connected cooling blades? A simple loose belt is all too common. When it gets too loose it usually gives a squeal when the alternator is trying to high charge just after starting. Not always though. You should not be able to turn the alternator by hand.