X-ray diffraction study of supercooled water has been performed using an imaging-plate X-ray detector down to -15 degrees C. The peak at similar to 10.8 angstrom, which grows with decreasing temperature, in the radial distribution function {D(r) - 4 pi r(2)rho(0)} indicates the existence of clathrate-like structures in supercooled water. It is suggested that anomalous properties of water, which become more pronounced at low temperatures, are closely linked to the development of clathrate-like structures in water at low temperatures. (c) 2008 Elsevier B.V. All rights reserved.