This is an irregular verb. It follows the conjugation pattern of the verb vencer.
This verb is mainly used in European Portuguese. In Brazilian Portuguese, umedecer is preferred.
Present:
A Ana humedece o pano antes de limpar.
Ana moistens the cloth before cleaning.
Preterite:
O Miguel humedeceu a terra antes de plantar.
Miguel dampened the soil before planting.
Conditional:
A Clara humedeceria a superfície ligeiramente.
Clara would moisten the surface slightly.