Structural studies of water have been made for a wide range of states but little work has been made for ¿stretched water¿, i.e. under negative pressure. This state may be investigated with the use of a Bertholet tube and some preliminary neutron experiments have already been made. By lowering the temperature, the liquid enters the doubly-metastable region [against T and P] and eventually undergoes cavitation nucleation with the production of transient ice phases. The intention is to investigate the structural behaviour of the liquid state from 20 to -15C along the isochoric line [constant density] and to determine the change in the H-bond network connectivity in the liquid state. The results will provide a critical test for current water potentials and the behaviour is also relevant to the transport of water in plants.