This chapter reviews the recent developments and refinements of analytical methods for preparing waters and other aqueous samples of different origins for the measurement of the oxygen and hydrogen isotopes by conventional dual-inlet, dynamic gas-source isotope-ratio mass spectrometry. The emerging techniques of continuous-flow mass-spectrometry are discussed as they are employed in both dual-inlet and continuous-flow mass-spectrometry. The size, chemical composition, and isotopic abundance of aqueous samples vary widely depending on their type, origin, and history. Automated gas equilibration methods are very suitable and are becoming standard techniques in many isotope hydrology laboratories. The increased analytical precisions are due to the subsequent development of modern gas-source isotope-ratio mass spectrometers with dual-inlets and multi-collectors, have caused the proliferation of new analytical methods and applications for the oxygen and hydrogen isotopic compositions of water. For natural hydrologic samples and new developments of continuous-flow mass spectrometry, it is possible to determine both δD and δ¹⁸O values, as they can provide two-dimensional information. The most significant progress in analytical techniques for stable isotope analysis of water is witnessed. Hence, overall quality control of isotopic data is becoming an important issue.