What is the story behind Sai Baba lighting lamps with water?

Chapter 5 recounts a remarkable miracle involving lamps. Sai Baba had a great fondness for lighting lamps in the mosque and temple, and he would personally go to local shopkeepers to beg for oil. After some time, the grocers conspired to stop this 'nuisance' and collectively refused to give him any oil. Baba returned quietly to the mosque, took the tin pot which had a tiny bit of oil, poured water into it, drank the mixture as an offering, and then filled the lamps with plain water. To the amazement of the watching grocers, he lit the dry wicks, and the lamps burned brightly all through the night, a testament to his divine power.