The Justitia (in red) was docked in the River Thames at Woolwich, close to the Royal Arsenal (termed the "Woolwich Arsenal" by Dr. Snow). The boat was located downstream from London, in a location where river water likely was polluted.  Case 12 may have dipped a bucket into the River Thames for washing and drinking.

Source: Wyld, J. A New Map of the Country Twenty-five Miles Round London. Published by James Wyld, Geographer to the Queen, Charing Cross East, London, 1872.