It is generally taken for granted that water is essential for life. Looking for water on Mars has been a preoccupation for decades, and there are an infinite number of meetings on the general topic of ‘water in biology’. Yet these rarely ask precisely why water is important. And if we cannot answer that question, then perhaps it might be replaced by some other medium in some other life form that can still metabolize and reproduce. In fact, there is recent evidence that the molecular–level requirements for water may have been overstated. Our Discussion Meeting aimed to take a constructively sceptical view, encouraging diversity of attitude by bringing together interested scientists from a range of disciplines.