I really don't like these nails, so much so I left cuticle oil on for the photo which I rarely do. I struggle with water marbling, and water spotting is a very similar technique. I didn't have any spray hand sanitiser, not sure if you can get it in the UK? I tried hairspray which didn't work. In the end I used acetone on an paintbrush to flick on to the water.
Base Polish: La Femme - Passion
Black Polish: Nails Inc - New York Noir