Water has evaporated from my tank, what now?

Distilled water is not good for tanks. Bottled spring water is best. Or just get a gallon jug, put the required amount of drops of aquarium conditioner in it, fill it up with water that's as close to the temp of the water in the tank as possible, and pour it in the tank. The chlorine remover works immediately but its best to put it in the container first, then add the water.