Condensible volatiles, water in particular, play crucial roles in determining the mass distribution and chemical composition of planets. Despite the central role of volatiles in planet formation, their distribution in disks is essentially unknown so far. We propose to use multi-wavelength spectra, from near-IR to sub-mm to measure the volatile molecular abundance profiles from terrestrial planet forming region to hundreds of AU. Using this method, we have successfully reconstructed the radial water abundance distribution in TW Hya protoplanetary disk. We find that high abundance of water vapor are concentrated in a narrow ring most likely located at the disk transition radius some 4AU from the central star. By combining the recent infrared spectroscopy with the unprecedented sensitivity of ALMA, the direct measurement of volatile distributions in significant samples is now within reach.