The phrase "original watercolor" refers to a unique artwork done with water-based paints. It means that there is only one of its kind, created by the artist's own hands, and is not a copy or reproduction of any kind. Full definition
Trio of Original Watercolor Paintings by Michelle Owenby Each painting is 6» x 6» 140 lb Cold Press Paper (chairish.com)
Original Artwork Painting is 12 «x12» 140 lb Cold Press Cotton Paper Archival Quality Original Watercolor Abstract Painting. (chairish.com)
In 2008, the brothers have appropriated original watercolors by Adolf Hitler to which they had added hippie motifs, and their work also carries references to William Blake's art, as well as the creations of Auguste Rodin and Nicolas Poussin. (widewalls.ch)