Water is a skin irritant which deserves attention because of its ubiquity. During the Vietnam war, soldiers suffered from painful swollen feet, so-called tropical immersion foot. In occupational dermatology, the importance of water as a skin irritant is especially appreciated. The irritancy of water has been demonstrated by occlusion experiments; occlusion with either closed chambers or water-soaked patches has been shown to produce clinical and histopathological inflammation. Functional damage, as revealed by increased transepidermal water loss, has also been shown. Repeated water exposure without occlusion caused an increase in blood flow on irritated skin; however, clinical evaluation did not show a difference in dryness or scaling. Several mechanisms such as osmolarity, pH, hardness and temperature might account for the irritancy of water. Extraction or dilution of natural moisturizing factors in the stratum corneum is another possible explanation. Occlusion per se also changes the physiology of skin and may trigger the activation of potentially active substances. However, much remains to be done to clarify the risk factors and mechanisms of water-induced irritation.