Our research compares three systems of continuous flow analysis coupled with cavity ring-down spectrometry (CFA-CRD) from Venice, Paris, and Grenoble laboratories for measuring water isotopes in ice cores, crucial for reconstructing past climate. We quantify each system’s mixing and measurement noise effects, which impact the achievable resolution of isotope continuous records. Our findings reveal specific configurations and procedures to enhance measurement accuracy, providing a framework to optimise water isotope analysis.