The paper exploits recent in-situ observations of water vapour in the lower stratosphere in the StratoClim campaign which was focused on the Asian Monsoon region, accepted as very important as providing a pathway from troposphere to stratosphere for important chemical species. The paper uses trajectory modelling to argue that, whilst very large water vapour concentrations were observed in some locations, significant further dehydration is likely as the air masses are transported, over tens of days, on a spiralling path into the main body of the stratosphere. The conclusion is therefore that these large water vapour concentrations do not imply a substantial moistening of the stratosphere. There has been a long-standing debate about the role of processes on different scales, from the cloud-scale to the regional scale, in controlling stratospheric water vapour, which has an important effect on the radiative balance of the troposphere. In combining in-situ data and trajectory modelling this study should help progress towards scientific consensus on this point.