Complex sentence: The Croton River was the main source of New York City's water supply from 1842 on, through the Croton Aqueduct, later called the Old Croton Aqueduct.
Split into simpler sentences: The Croton River was the main source of New York City's water supply from 1842 on. It was brought to the city through the Croton Aqueduct, which was later called the Old Croton Aqueduct.