The development of a better understanding and a predictive model for water influx is pivotal in scaling up the linked vertical well UCG process, since water influx strongly affects gas quality. A water-influx model is developed here which incorporates radial permeation of water throng the coal seam, and steam generation by spalling enhanced drying of the coal and overburden. This random spalling process which enhances drying by exposing fresh wet surface is described by a surface-renewal model. A cavity-growth model based on coal consumption ties together these mechanisms. The model predictions are found to agree quite well with the measured daily and total water influx for the available field tests.