Water can leak in from multiple places. If boat is on trailer just fill up each bait well and see if any water gets into the bilge while on the trailer and of course not raining on the boat. Hatches, cover plates, cracked or loose hoses, though hulls and unseen cracks can all leak water into the bilge. Visually inspecting the bilge while on the water usually can give you a clue as to how the water is getting into the vessel.
Jim