The evapotranspiration tank (TEvap) is a 'zero-discharge' ecotechnology for toilet water disposal. This work refers to a preliminary study to evaluate the influence of forages and the addition of a vertical soil strip on evapotranspiration (ET), electrical conductivity (EC) and pH in TEvap receiving fresh water. The factors studied were the forages and the soil strip, resulting in four treatments with three replications. Two plant growing seasons, cycle 1 and cycle 2, were monitored, during which the variables were measured every three and seven days, respectively. Weather variables were used to estimate the reference evapotranspiration and determine the TEvap coefficient (KTEvap). The accumulated ET for TEvap with Capiaçu was 27.93% and 45.89% greater than for TEvap cultivated with Tifton-85 during the first and second cycles, respectively. There were no significant differences in ET for TEvap with and without the soil strip. BRS Capiaçu also showed lower values for EC and pH. High values were obtained for KTEvap: 2.37 and 1.76 for TEvap cultivated with BRS Capiaçu and Tifton-85 grass, respectively. Considering the period of this study, the minimum area for 'zero-discharge' would be 5.70 m2 inhab-1 and 7.77 m2 inhab-1 by TEvap planted with BRS Capiaçu and Tifton-85 grass, respectively. Due to its greater capacity for evapotranspiration, it can be concluded that the BRS Capiaçu forage is suitable for a 'zero-discharge' constructed wetland systems. It is suggested that further, more-thorough studies be carried out to design a 'zero-discharge' TEvap, considering different weather conditions, crops and inlet toilet water.HIGHLIGHTS Evapotranspiration tank (TEvap) is a 'zero discharge' ecotechnology for disposing toilet water;A preliminary study was conducted to simulate the evapotranspiration in TEvap receiving fresh water;Two forages - Cynodon spp. (Tifton-85 grass) and Pennisetum spp. (BRS Capiaçu) - were cultivated in the tanks;5.70 m2 inhab-1 were estimated for evapotranspiration with BRS Capiaçu and 7.77 m2 inhab-1 with Tifton-85 grass.