Many minerals incorporate water directly into their structure as molecular water (H2O) or hydroxyl (OH). The oxygen (16O,17O,18O) and hydrogen (H,D) isotopes of hydrated minerals are a potentially rich source of information about the environmental conditions under which hydrated minerals form and/or interact with fluids after deposition. As part of a 5-year European Research Council project, my group has been developing the use of triple oxygen and hydrogen isotopes of structural water contained in hydrated minerals as a paleoclimate proxy. We are pioneering new methods for measuring d18O, d17O and dD in hydrated minerals by combining thermal gravimetric analysis and cavity ring-down laser spectroscopy. I will specifically discuss the merits and uncertainties in combining measurements of d18O of biogenic carbonates and triple oxygen and hydrogen isotopes of hydration water in gypsum (CaSO4·H2O) in lake sediments cores to estimate past changes in temperature, rainfall and relative humidity on the Yucatan Peninsula, Mexico.