The underlying problem is often the stem of the Nivito faucet. If the stem is stripped, the handle will be loose and may spin on its end. If the stem is worn, you can try tightening it with Teflon pipe thread tape. If you're unable to get the screw to tighten, you may need to use a special plumber's wrench. If this doesn't work, you can always apply permanent thread sealant to the screw.