Backfilling, which is an example of the clean use of mineral resources, allows a safe work environment and provides a disposal means for mine tailings. Safe mining is significantly influenced by the durability of paste backfill material, which can be affected by water. In this study, the effect of water on the mechanical properties and permeability was experimentally examined with increasing curing time in the Taiping Coal Mine, China. The interaction of paste backfill material with water results in an exponential increase in the weakening coefficient with increasing curing time, and a linear decrease with higher water content. Slaking, a process in which cohesion is lost under the effects of water and physical disintegration, occurs in paste backfill material. Low hydraulic conductivity is found, which contributes to the durability of paste backfill material. Microscopic analysis shows that porous and nonuniform distributed structures account for the weak permeability and stable strength. On this basis, a durability classification chart for clean use is proposed; this classification scheme identifies three grades of durability affected by water. The engineering geological characteristics of each grade are provided, providing guidance for identifying the type and grading of durability of paste backfill material affected by water in coal mining. The approach was validated by successful application.