<p>The design and operation of constructed wetlands for wastewater treatment depends, inter alia, on their water balance, which is, in turn, dependent on precipitation and water loss via evapotranspiration. This work outlines a comparative water loss assessment of vegetated Sealed Mesocosms (evapotranspiration, ET) and their respective controls (evaporation, Ev) for urban wastewater treatment in a coastal semi-arid Mediterranean climate. Potential evapotranspiration (PET) is estimated at 2431&#xa0;mm.year⁻¹, with a daily average of 6.659 ± 4.168&#xa0;mm.day⁻¹, and is much more closely linked to dry winds, reducing average relative humidity. Average of the evapotranspiration capacity of the atmosphere (ℇ) is measured 17.41 ± 15.30&#xa0;mm.d⁻¹; planted SFCW-mesocosms (surface flow constructed wetlands) have the highest actual evapotranspiration (AET), 23.21 ± 15.54&#xa0;mm.d⁻¹. Planting mesocosms does not generally result in significant changes in daily AET, whereas during the vegetative period, ℇ in most mesocosms is significantly higher with respect to vegetative rest. The AET of <i>Arundo donax</i> mesocosms and the SFCW second-level <i>Phragmites australis</i> mesocosms exceed twice the Ev of their respective controls. <i>Lemna gibba</i> exceptionally produces 4.702&#xa0;g of dry matter per liter of ET water loss, provided the biomass is harvested regularly over the year. The results of this study will help guide the design of extensive wastewater treatment processes in Mediterranean climates, depending on the context of applied water restitution and/or macrophyte biomass valorization.</p>