if you want vasemode to be watertight then you may have to pore some lacquer to fill the gaps. I never use water in my 3d print if i have used vase mode. Even when I use normal 3d print settings I have problem to make it watertight. If you Zoom in the vase in your slizer, then you could see why its not watertight.
https://blog.prusa3d.com/watertight-3d-printing-pt1-vases-cups-and-other-open-models_48949/