Served by one of London's many underground streams, the water was praised for being "bright, sparkling, and cool, and of an agreeable taste".[4] These qualities were later found to be derived from decaying organic matter from adjoining graveyards,[4] and the leaching of calcium from the bones of the dead in many new cemeteries in north London through which the stream ran from Hampstead.[5] Several hundred people died during what became known as the Aldgate Pump Epidemic,[5] and on its relocation in 1876, the New River Company changed the supplies to mains water.

(http://www.autoadmit.com/thread.php?thread_id=3924718&forum_id=2#35653342)