What most naturally follows?

How to plump raisins
Combine the raisins and liquid in a saucepan.
Place the raisins inside a small saucepan. Pour water into the saucepan as well, using just enough to completely cover the raisins.
Water works well as a default option, but for something more flavorful, experiment with other liquids. For instance, consider trying grape juice, orange juice, or another fruit juice.