The world’s first continuous flow isotopic TIC/DOC-CRDS measurements are reported here with remarkable achieved precisions. A measurement precision of the isotopic ratio in the range of 0.2 ‰ to 0.4 ‰ was achieved in minutes of measurement time. Such precision readily distinguishes the isotopic DIC and DOC signatures from a set of three different streamwater samples collected from various sites in Northern California. The current TIC/DOC-CRDS setup will enable shipboard measurement and presents a rugged, portable and inexpensive analytical instrumentation alternative to the traditional use of methods based on the more complex and lab-confined isotope ratio mass spectrometry technique.