The yields of the dissociation products of water ionized by fast proton impact were measured relative toH2O+using the coincidence time-of-flight method. The relative yields following single ionization were found to be independent of the collision velocity over the range of collision velocities measured and similar to the values reported for ionization by equal velocity electron impact, except for a higher rate ofH2+production. Double ionization of water leads predominantly to two dissociation channels, namelyH++OH+andH++O++H,which are equally likely and also independent of the collision velocity. TheO2+fragment was found to be always in coincidence withH+,thus suggesting it is only a product of triple (or higher) ionization of water. ©2001 American Institute of Physics.