In normal water, about 1 molecule in 3,200 is HDO (one hydrogen in 6,400 is D), and heavy water molecules (D2O) only occur in a proportion of about 1 molecule in 41 million (i.e. one in 6,4002)....Experiments in mice, rats, and dogs[26] have shown that a degree of 25% deuteration causes (sometimes irreversible) sterility, because neither gametes nor zygotes can develop. High concentrations of heavy water (90%) rapidly kill fish, tadpoles, flatworms, and Drosophila. Mammals, such as rats, given heavy water to drink die after a week, at a time when their body water approaches about 50% deuteration....Because it would take a very large amount of heavy water to replace 25% to 50% of a human being's body water (which in turn is 65-70% of body weight) with heavy water, accidental or intentional poisoning with heavy water is unlikely to the point of practical disregard. For a poisoning, large amounts of heavy water would need to be ingested without significant normal water intake for many days to produce any noticeable toxic effects.
According to that article martian water has 5 times more D than water on earth. Comparing that with the Wikipedia data, it does not seem to be a showstopper at all. Not more than 6 month zero gravity.
