"Mealy's father was a waterman"
Watermen earned a living from the river, and they usually lived near or on the water.  

A waterman was considered a lowly sort of being, and Charles Dickens later explored its social connotations in his last completed novel, Our Mutual Friend (1864-1865), which features the character of waterman Gaffer Hexam, who robs corpses floating in the Thames.