How can we tell if it’s a polyurethane finish?

Q: A friend of mine has a house that was built sometime in the 1940’s. She and her realtor are unsure as to whether or not her hardwood floors have a polyurethane finish. Is there a way that we can check?

A: It probably is wax. Put a few small spots of water on it and let it sit for 10 minutes. If it leaves a spot it is wax.