Can you explain the story of how Sai Baba lit lamps with water when the shopkeepers refused him oil?

According to the narrative in Chapter 5, Sai Baba had a great fondness for lighting lamps in the temple and mosque, and would daily beg for oil from local shopkeepers. One day, the grocers conspired to refuse him, calling his request a nuisance. When they all said no, Baba returned to the mosque with his tin pot containing a minuscule amount of oil. He poured water into it, drank it as an offering, and then filled the lamps with plain water. He lit the water-soaked wicks, and to the amazement of the watching grocers, the lamps burned brightly all night without any oil. This miracle caused the grocers to feel deep repentance for having lied to and troubled Baba.