Sargent and Isabella Stewart Gardner shared a lifelong love of Venice. Both visited the city repeatedly and knew it well. This view, as many others, was painted by Sargent from a gondola. Perhaps looking at this picture, Gardner remembered one of her own gondola rides on Venice's canals. She purchased it many years after her last visit to the lagoon city.
Source: Oliver Tostmann and Anne-Marie Eze, The Inscrutable Eye: Watercolors by John Singer Sargent in Isabella Stewart Gardner’s Collection, exhibition on view in the Museum's Fenway Gallery, October 31, 2013–January 20, 2014.