The dehydration of calcium alginate beads is observed to have a simple power-law time dependence. The ratio of the water content, M(t), to the initial water content, M-0, can be expressed as M(t)/M-0 = (1 - t/t(c))(3/2) The parameter t(c) is insensitive to the guluronic content of the alginate or the degree of cross-linking. Using this simple model, t(c) can be estimated from the properties of water vapor, the initial water content, and the relative humidity, in addition to an empirically derived correction factor, K, which has been found to be 2.8 +/- 0.3.