Water displays a highly complex phase diagram that is key to a range of critical processes, from the evolution of icy moons to that of the Earth's hydrosphere and even of life itself. Using ISIS facilities, we have recently shown that the water phase diagram is hypersensitive to ammonium fluoride doping which leads to the complete disappearance of the hydrogen-ordered ice II from the phase diagram. This phenomenon can be explained on the basis of the topologically constraint nature of ice II and the incompatibility of ammonium and fluoride ions with the ordered local structure. Building on this exciting finding we now need to further map the phase diagram of ND4F/ice mixtures and to investigate the effect of ND4F on the hydrogen ordering phase transitions from ice III to IX and ice VII to VIII. These experiments will give new insights into the origins of the complexity of condensed H2O.