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 model is developed here which incorporated radial permeation of water through the coal seam, and steam generation by spalling- enhanced drying of the coal and overburden. This random spalling process which enhancces 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 influc for the avaliable field tests.