The composition of impurities in ice controls the stability of liquid water and thus the distribution of potential aqueous habitats. We present a framework for modeling the brine volume fraction in impure water ice as a simple polynomial function of temperature and bulk ice salinity, inspired by models originally developed for sea ice. We applied this framework to examine the distribution of brine within the thermally conductive layer of Europa’s ice shell, considering binary (NaCl and MgSO4) and analog (Cl-dominated and SO4-dominated) endmember impurity compositions. We found that the vertical extent of brine in a conductive ice layer, expressed as a fraction of the total layer thickness, is more sensitive to composition for the binary endmember impurity compositions than for the analog endmember impurity compositions. Although the vertical extent of brine is equal for the analog endmember impurity compositions, the brine volume fraction is consistently higher for the Cl-dominated ice shell than the SO4-dominated ice shell. Pressure, governed by the ice thickness, was found to have only a minor effect on the vertical extent of brine within an ice shell, relative to temperature and bulk salinity. The minimum stable bulk ice shell salinity formed through freezing of an ocean was found to be insensitive to composition and ultimately governed by the magnitude of the assumed percolation threshold.