Look at the paint you want to identify. If it sits along with other small, hard, dry circles of pigment enclosed in a case, you have water colors. These pigments are water based and create transparent washes of color when diluted.
Pick up the tube of paint you want to identify. Read the label if there is one. If the label contains the word "Acrylic," or "Gouache," it's a water-based paint. If the label reads "Oil Paint" or "Oils," your paint is oil based.
Test the paint itself if there is no label available or if it is illegible. Squeeze out about an inch of paint onto a palette. Use your paintbrush to smear the paint against the surface.
Fill the mason jar with water. Put your paint-covered brush in the jar. Swirl the brush around the jar. If the paint thins out leaving a clean brush, it is not a traditional oil paint. If the paint sticks on to the brush, then it is a traditional oil paint.
Test whether the paint is a water-based paint, or a water-soluble oil paint; paint a few brush strokes on to a canvas board. Leave it alone for two hours. If the paint is completely dry after the two hours, it is a water-based paint. If the paint is still wet or sticky, it is a water-soluble, oil-based paint.