Q. Is it possible to reuse the old floating diya?

Answer

Yes you can reuse it! But we observe that many folks don't want to deal with their old diyas. After Diwali they are discarded in preparation for the next year's purchase of new ones. I don't see the point of throwing. Oh why? Please keep them for the entire Diwali celebration. Girija Kadam reflects on her youth and says "In those days people didn't have much money. The diyas were painted every year and kept for many celebrations. Wastefulness is a widespread problem among modern humans.