The present study investigated the influences of water ingress on the electrical resistivity and electromechanical sensing responses of CNT/cement composites. The water absorption, mechanical, electrical, and electromechanical sensing characteristics of the composites were assessed in terms of water absorption rate, compressive strength, electrical resistivity, tunneling-induced electrical resistivity, fractional change in the resistivity (FCR), and R-squared value. The water absorption rate increased, and compressive strength decreased as the CNT content and water-to-cement ratios increased. These were ascribed to an addition of the dispersion agent and water which caused microstructures of the composites more porous. In addition, the tunneling-induced electrical resistivity test exhibited that the tunneling effects became more pronounced with increase of the CNT and water contents. In electromechanical sensing test, FCR value reached the highest level at CNT content 0.2%, and R-squared value enhanced as water ingress was reduced. In this regard, it can be concluded that the new types of materials with high hydrophobicity are necessary to improve the stability of the electrical electromechanical sensing capability of the CNT-based cementitious sensors as exposed to the water conditions.