How Sai converted water to oil ?

Sai Baba was very fond of oil lightings. He used to go to oil merchants and ask them for oil. On fetching oil from them he lit the lamps for the whole of the nights. This went on for somedays. One day the oil merchants refused to give oil to baba. Baba then went back with out getting disappointed. He had a few drops of oil left in his vessel. he mixed the oil left with water and drank the same. He then spit the water mixed with oil back in the vessel and lit the lamps. The merchants who were watching all this from a distance were taken aback, realised their mistake and begged baba to forgive them. Baba then accepted their apologies and preached them to always stick to the truth.