Delamination of solar module interfaces often occurs in field-tested solar modules after decades of service due to environmental stressors such as humidity. In the presence of water, the interfaces between encapsulant and the cell, glass, and backsheet all experience losses of adhesion, exposing the module to accelerated degradation. Understanding the relation between interfacial adhesion and water content inside PV modules can help mitigate detrimental power losses. Water content measurements via short wave infrared reflectometry combined with 180° peel tests were used to study peel test samples exposed to damp heat and dry heat conditions. The effect of temperature, cumulative water dose, and water content during peel tests on interfacial adhesion was studied. Temperature and time decreased adhesion at all interfaces, whereas water content at time of measurement showed significant decreases in strength for the backsheet/encapsulant interface. Water dose showed little effect for the glass/encapsulant and backsheet/encapsulant interfaces, but there was significant adhesion loss with water dose at the front cell busbar/encapsulant interface.