Can floaters get worse if dehydrated?

No. Floaters represent the natural aging process of the vitreous gel. Dehydration will have no impact on floaters. The sudden onset of new floaters or floaters accompanied by flashing lights like july 4 sparklers could signal the beginning of a retinal detachment and should be immediately evaluated by your eye md.
No. Any new or worse floaters require a dilated retinal exam to rule out retinal tears or retinal detachments.