This work evaluated the results of water absorption tests on specimens of expanded polystyrene (EPS) in the specific masses of 10, 20 and 30 kg/m³ molded in specimens with cubic dimensions of 100 mm. The tests were carried out according to ASTM C272 (2001). Long-term water absorption tests were also performed, which differs from the simple test by the immersion time of the specimens, in which the test bodies were kept submerged for a period of 28 days, seeking to study the behavior of the EPS when exposed or in contact with water for long periods of time. From the results it was observed that the water absorption parameters tend to decrease with the increase of the specific mass, being that the lower density presents significant water absorption, this shows that there is a loss of the beneficial characteristics of the use of EPS with low density. Thus, it is important to provide a waterproofing system in practice that avoids the direct contact of the geofoam with the water, as well as an adequate and efficient drainage system to remove the water in contact with the EPS faster in the construction. It is also worth noting that water absorption represents about 4% of the sample volume and the behavior, both in mass and volume, for immersion in a 24-hour period and 28 days remains similar.