I recently water marbled my nails and here's how it was done.
First, here are the thing I used:
-3 nail polishes in purple, orange, and white
-A small container filled with cold water
-A toothpick or wooden skewer
-thick cream lotion or vaseline
I prepared my finger by rubbing the thick lotion of half way down my finger and all around my nail. Doing this makes it easy to remove the excess polish off of your finger. Next, I place drops of nail polish in the water. First, I placed a drop of white polish and then a drop of orange, purple, white, and orange again.
Next, I took the skewer and made line from the center outwards, until I achieved my desired look.
Next, I placed my finger in the water, nail side down. While my nail was in the water, I took the skewer and swirled in the water to remove the excess polish. Once all polish was removed from the surface of the water, I removed my finger.
I waited a few minutes for the polish to dry and wiped the excess polish from my finger. Here's the finished result: