One strategy is called cyclic release of carbon dioxide. This has been well studied in pupae of Hyalopohora cecropia , a large insect suitable for study in this regard. Carbon dioxide is allowed to build up in the trachael system for a long as seven hours, then is released in bursts during which the spiracles are wide open. Between the bursts of carbon dioxide release the spiracles are not closed as tight as possible, but rather flutter so as to allow a continuous uptake of oxygen. While the cuticle and control of the spiracles serve to restrict the loss of water, a certain amount of water is inevitably lost.
Most insects take in sufficient water with the food they eat.
In his book on insect structures and function, Chapman thought some insects may select food with a higher water content under certain circumstances. Still other insect species may consume more food than they actually need in order to realize the potential water in the food. Moreover, many insects drink water. The dipteran Phormia , for example, has specific water receptors in the tarsal and labellar sensilla. I've often observed wasps drinking water in desert pools in Mexico.