Measurements of water group ions at Comet Giacobini-Zinner are analyzed which have been obtained with the EPAS instrument on the ICE spacecraft, in order to determine the bulk parameters of these ions. The measured ion velocity distributions are extrapolated to zero energy and integrated to obtain estimates of both number and thermal energy density. The number density is compared to independent observational and theoretical estimates. Combining the EPAS results with magnetic field and plasma data, the beta and Mach numbers of the flow have been obtained in the region surrounding the comet.