In sol-gel you are using some additives (usually surfactants) that have a different interaction with the hydrated salt, comparing to the dehydrated one. Anyway, when solving the salt into your aqueous solvent hydration occurs but, according to the pH the hydration no. in aqueous solution is 6, 4, 2 or 0 (the hydration no decreases by increasing decreasing pH).

To answer to your question, the easiest way to dehydrated your salt is to dry it in an oven at about 120oC. Than keep it in a dry environment.