Confining water in lab synthesized nanoporous silica matrices MCM-41-S with pore diameters of 18 and 14 Angstrom, we have been able to study the molecular dynamics of water in deeply supercooled states, down to 200 K. Using quasielastic neutron scattering and analyzing the data with the relaxing cage model, we determined the temperature variation of the average translational relaxation time and its Q-dependence. We find a clear evidence of an abrupt change of the relaxation time behavior at Tapproximate to225 K, which we interpreted as the predicted fragile-to-strong liquid-liquid transition.(C) 2004 American Institute of Physics.