The classical watercolor medium is #63300 Gum Arabic.
Heat the distilled water (#65000) in a double boiler and add the Gum Arabic (#63300).
Stir occasionally until the Gum Arabic crystals are dissolve d completely .
You can use any Color Concentrates or choose a pigment according to your technique: use transparent ones if you prefer light washes, and opaque ones for gouache.
Mix pigments into a thick paste with the Gum Arabic solution and dilute with water for use as needed.
As needed: Add 1/2 part of Glycerol (#64900) as a plasticizer. This keeps the finished paint from becoming too brittle and cracking. Add more if you plan to pour the paint into pans, so they retain some moisture .
Gum arabic in pieces is often contaminated, either put the the pieces in tights, which will hold back the impurities while the gum arabic will go into solution or filter after dissolving!