Sentence:  Argiento had been trained so rigorously by the Jesuits that Michelangelo was unable to change his habits : up before dawn to scrub the floors , whether they were dirty or not ; water boiling on the fire for washing laundry every day , the pots scoured with <WSD>river</WSD> sand after each meal . 
Meaning of the word marked with <WSD> tags:  a large natural stream of water (larger than a creek)