Dietary water intake in penultimate two instars of silkwormBombyx mori and eri silkwormPhilosamia ricini fedad libitum on mulberry leafMorus alba and castor leafRicinus communis respectively at 26±2°C is reported. The lower ration level results in accumulation of water content in the body of insects. The water retention efficiency (per cent of absorbed water retained in the body) increases with the decreasing ration level. The larva retains higher amount of water in the body by increasing water retention efficiency from 22% at 100% ration to 61% at 25% ration. This is an important adaptive mechanism exhibited by larvae. The water utilization budgets are discussed with the budgets available for other insects.