Soil-geotextile systems are often subject to water infiltration due to natural weather variations. When the water penetration resistance of the geotextile leads to the accumulation of water at the soil-geotextile interface, a serious problem of instability in the geotechnical structure may occur, especially in thin layers of soil such as landfill covers. Most nonwoven geotextiles have a water penetration resistance greater than 5 mm when completely cleaned and composed only of hydrophobic filaments/yarns. The evaluation of the resistance offered by the geotextile to water penetration can be useful to understand the interaction between water and geotextiles under unsaturated conditions. The purpose of the present article is to discuss the different test procedures found in the literature for the determination of water penetration resistance of geotextiles. Experimental data are presented to illustrate the affinity of geotextiles with water under different conditions. This paper also presents an evaluation of the current state of knowledge regarding the hydrophobic/hydrophilic properties of geotextiles under unsaturated conditions. Often, geotextiles are used as filters, separators, or drains without proper verification of some of the basic principles for selecting and installing the product, and thus some minimum and important requirements may be ignored. Although in most cases there are no serious problems, sometimes the accumulation of a few centimeters of water over drainage systems may compromise the stability of geotechnical structures if this condition is not considered in the design. It has been observed that some of the test procedures reviewed do not take into account the hydrophobic/hydrophilic characteristics of the geotextiles.