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Water is an essential resource affecting behavior and the acquisition of energy, especially in environments where water is spatially or temporally restricted or unavailable. Recent investigations have shown that several species of marine snakes dehydrate at sea and are dependent on environmental sources of fresh water to maintain water balance. However, in this context, little is known concerning the majority of ’true’ sea snakes (Hydrophiini). We investigated the dehydration and drinking responses of five species of hydrophiin sea snakes collected during the dry season in northern Australia. None of these snakes drank sea water, even when dehydrated. Dehydrated individuals of Hydrophis curtus, H. elegans and H. zweifeli drank fresh water, and the mean threshold levels of dehydration that first elicited drinking were deficits of -26, -29 and -27% of body mass, respectively. Individuals of Aipysurus mosaicus and H. peronii did not drink fresh water when similarly dehydrated. Few snakes that we collected following > 4 months of drought drank fresh water immediately after capture. Hydrophiin species appear to have a high resistance to dehydration, which they evidently tolerate in marine habitats for extended periods during drought. Thirst in these species is significantly less sensitive than in other species, suggesting that marine snakes have variable requirements for drinking fresh water. These data illustrate that sea snakes are characterized by diverse responses to dehydration and likely have different osmoregulatory strategies for survival, with implications for better understanding the evolutionary success of secondarily marine vertebrates and their potential responses to future changes in tropical precipitation.