The rate, V, of the water absorption process and the intensity, I, of ultraweak luminescence (UWL) emitted by imbibing grain of Polish spring wheat of Henika variety were measured and compared. The study was realized for the grain swelling completely submerged in distilled water during eight-hour time periods at temperatures of 288 K, 303 K and 338 K. The rate V was estimated measuring the mass gains in the series of grain samples after the planned time. I was registered in the spectral region between 360 nm and 760 nm using a high sensitivity photo-electronic apparatus working in the single-photon-counting mode. The obtained data were presented as the dependencies of V on t, I on t, and I on V, where t is the swelling time. The dependence of the intensity I on the rate V was characteristically changed after given time period of grain soaking. This time was postulated to be the time necessary for water penetration through the seed coats or through the seeds coats and aleuronic layer. Then, determining such characteristic changes in the obtained dependencies between I and V, the times of water penetration through the seed coats were estimated at three temperatures.