<p>Water accumulation in bridge cables or hangers caused by sealing failures poses a significant threat to structural integrity due to corrosion. This study introduces a novel non-destructive method using magnetostrictive guided waves to quantify water accumulation in bridge cables or hangers to enhance structural health monitoring. By analyzing the reflection and transmission properties of elastic waves at solid-liquid interfaces, the method employs longitudinal wave modes to optimize detection parameters. Finite element simulations and laboratory experiments on a cable validate the approach, showing an exponential decay in guided wave echo amplitudes and a linear increase in attenuation coefficients with increasing water accumulation length. Field tests on a tied-arch bridge confirm the method’s efficacy with results verified. This approach offers significant improvements over invasive techniques which would provide a sensitive and efficient tool for monitoring the cable and hanger conditions.</p>