"Water is fundamental to life as we know it, and the current strategy for the search of life on Mars is to “follow the water”. Much of the water on Mars exists today in the form of hydrated minerals that incorporate molecular water or hydroxyl into their crystalline structure. Hydrated minerals provide a tool for studying the past history of the hydrosphere on Mars as well as Earth. Oxygen and hydrogen isotopes of hydration water in minerals record information about the conditions under which the minerals form and subsequently interact with fluids after deposition. This proposal outlines the technological and scientific basis for a new approach to the isotopic study of hydration water in minerals and mineraloids. The recent availability of tunable diode lasers now permits the measurement of water isotopes by laser absorption spectroscopy at a precision equal to or better than conventional methods. This development opens new opportunities for studying the isotope composition of mineral hydration water in novel ways, which hitherto has been difficult or impossible. I propose a five-year program to establish a research group at the University of Cambridge to study the nature of water isotopes in hydrated minerals: (1) how many different types of hydration states of water are present and how they are fixed into the mineral structure; (2) how the isotopic composition varies among the differently bound water in minerals; (3) how the type of bonding of water in minerals affects the rate of isotopic exchange with external water; and (4) whether or not any of the hydration water has retained its isotopic composition from the time of formation. The project will include both a theoretical (ab initio simulations) and empirical approach that has the potential to transform our understanding of mineral hydration water and its isotopic composition. The research has wide ranging application for addressing fundamental problems across many disciplines in Earth and Planetary sciences."