A non-return hot water diving suit in which hot water is supplied to keep the diver warm is exhausted from the suit through a single outlet valve, readily accessible to the diver. In the event of failure of the hot water supply the valve can be quickly closed, trapping the existing hot water in the suit and extending the length of time available for the diver to return to safety. In the preferred form the valve is combined with a flow controlling baffle, which will allow normal hot water outlet flow, but inhibits sudden or rapid intake of cold water through the open outlet.