We present contact angle measurements of water on single-crystal rutile TiO2 0 10) surfaces, exposed to ambient air, or protected in dry air. Our measurements indicate that the surfaces exposed to ambient air are hydrophobic, with a contact angle of theta = 61(5)degrees. However, the well-protected dry surface also exhibits some hydrophobic tendency, with theta = 32(5)degrees. It is known that UV irradiation transforms both surfaces superhydrophilic, with theta=0 degrees IR. Wang, K. Hashimoto, A. Fujishima, M. Chikuni, E. Kojima, A. Kitamura, M. Shimohigoshi, T. Watanabe, Nature 388 (1997) 431-432]. We also present preliminary X-ray crystal truncation rod measurements on the hydrophobic TiO2 (110) surface, and of the effect of UV illumination on the surface. Published by Elsevier Ltd.