If you are consistently clinically dehydrated (really, really dehydrated, like you just crawled in from the desert where you were dying of thirst), it might theoretically reduce your semen volume, just the way it would reduce your blood or tears.
If you're asking because you know for a fact (because you measured) that you used to produce more volume, and now you have measured again and aren't producing as much, for that question see your doctor.