The Picarro L2140-i is a state-of-the-art Cavity Ring-Down Spectroscopy (CRDS) analyzer specifically designed for high-precision measurement of water isotope ratios. It simultaneously quantifies hydrogen-2 (δ²H or δD), oxygen-18 (δ¹⁸O), and oxygen-17 (δ¹⁷O), and uniquely determines ¹⁷O-excess. This instrument is essential for detailed studies in hydrology, paleoclimatology, and atmospheric science, providing a comprehensive isotopic fingerprint of water samples, including plant and soil water. Utilizing patented CRDS technology, the L2140-i delivers exceptional precision, achieving 15 per meg or better for ¹⁷O-excess, a level previously limited to complex Isotope Ratio Mass Spectrometry (IRMS) systems. The analyzer exhibits minimal drift, typically requiring calibration only once per day, and can also measure water vapor concentration. It offers flexible measurement modes to optimize throughput: Standard mode processes 27 samples per day, Express mode handles up to 50 samples per day with high precision, and Survey mode allows for rapid approximations of isotopic values for up to 900 injections per day, ideal for large sample batches and memory effect reduction. Typical precision for δ¹⁸O is <0.025‰ and for δD is <0.1‰. This analyzer is critical for enhancing the understanding of present-day climate, reconstructing past climates, and investigating the intricate interactions between the hydrosphere and biosphere. Its applications span paleoclimatology, (eco)hydrology, atmospheric science, oceanography, geochemistry, biochemistry, and meteorology. The L2140-i provides a simpler, more affordable, and highly precise alternative to traditional IRMS for water stable isotope analysis, making advanced isotopic research more accessible. The L2140-i is compatible with a suite of peripherals to accommodate various sample types and research needs. These include the A0325 liquid autosampler, A0211 vaporizer, and the A0214 Micro-Combustion Module (MCM) for removing organic interferences. The A0213 Induction Module (IM) is available for analyzing matrix-bound water from solid materials like plant leaves and soil, especially those with high total-dissolved solids. Other accessories include the A0217 Continuous Water Sampler (CWS) and the A0101 Standards Delivery Module. The instrument also includes ChemCorrect™ post-processing software for flagging contamination and normalizing measurements, ensuring data quality. Water can be introduced directly as vapor or through vaporization of liquid samples.