Abstract <p>While the integration of treated wastewater in cementitious composites offers a vital pathway for sustainable construction, its widespread adoption hinges on the reliability of standard quality control mechanisms. This study investigated the acoustic and mechanical invariance of standardized mortars produced with potable water (Mix 1), secondary-treated wastewater (Mix 2), and tertiary-treated wastewater (Mix 3). Rather than merely assessing material performance, this research validates the robustness of ultrasonic pulse velocity (UPV) as a nondestructive testing (NDT) tool that requires no specific recalibration for alternative water sources. Monitoring over a 90-day curing period revealed that the fundamental constitutive relationships between the wave velocity, density, and mechanical strength remained unaffected by the water quality. The experimental density adhered strictly to the reference models (<i>R</i>² = 0.99), and a unified regression analysis demonstrated that a single predictive model accurately estimated the compressive strength (<i>R</i>² = 0.96) and static modulus (<i>R</i>²&#xa0;= 0.99) for all mixture types. The absence of statistically significant stratification between water sources (ANOVA, <i>p</i> &gt; 0.97) confirms that the treated wastewater does not alter the micromechanical signal propagation characteristics. Consequently, this study establishes that existing standardized NDT frameworks are directly applicable to wastewater-based mortars, thereby removing a significant technical barrier to their industrial implementation.</p>