Fun Riddles

To anyone actually reading this, and my own enjoyment...All answers are backwards so you have time to guess before your brain recognizes it.

A man has a bucket that weighs twenty pounds. He puts something into the bucket to make it lighter... what is it?

(eloH A)

To keep me, you must give me. What am I?

(droW ruoY)

Which word in the English language becomes shorter when it is lengthended [with er]

(retrohS)

The buyer doesn't use it, the seller doesn't want it, and the user doesn't see it. What is it?

(niffoC A)

Food helps me, but water hurts me, what am I?

(eriF)