Catharanthus roseus roots readily as spring/summer cuttings, and I wonder how it will do at this time of year. If you decide to try it, be sure that you prepare the cuttings properly and insert them into a porous, fast draining potting medium. (Not 'dirt', as out of your garden.) Perhaps bottom heat at this time of year would be helpful.

I can't speak to the success of propagating them in water as I don't root anything that way.