Like many living creatures, water is an essential part of a caterpillar’s diet. However the caterpillar gets its water from what it eats rather than drinking it from a pool or container of water. If you think a caterpillar you’re keeping looks a little dehydrated, spray the leaves with water before adding them; the droplets left on the leaves will be sufficient for the caterpillar. Always give the caterpillars quality foliage to eat; there is no need to add a small container of water to the caterpillar enclosure (in fact it might harm the caterpillar if it falls into the water).