ABSTRACTThe Bowen ratio, defined as the ratio of sensible to latent heat flux, is crucial for quantifying land‐atmosphere energy exchanges and evaporation rates from terrestrial surfaces. Despite extensive research on the Bowen ratio over placid water surfaces (e.g., lakes), further investigation is needed to understand its dynamics in small reservoirs subjected to water inflow/outflow (i.e., surface flows) and wind. To address this knowledge gap, the evaporation rate and the sensible heat exchanges are measured between the water surface and overlying air in a small laboratory basin under different water surface flow rates (1.0–10.5 l min−1) and wind speeds (0–2.0 m s−1). Three different wind flow conditions are explored: no wind, headwind (opposing the water surface flow), and tailwind (aligning with water surface flow). The findings indicate strong correlations between sensible heat flux, water surface flow rate, and wind speed, particularly under headwind conditions. Nevertheless, concerning the latent heat flux, the measurements demonstrate that for each wind condition, the evaporation reaches its minimum value in a certain water surface flow rate, resulting in the highest value of the Bowen ratio. To facilitate the application of these laboratory findings for estimating the Bowen ratio under real environmental conditions, mathematical relationships using dimensionless numbers obtained through non‐linear regression analysis are established. The results exhibit a good agreement with measurements in a small water basin.