Capture zone delineation is indispensable in all wellhead protection programs for the safeguarding of groundwater supplies. Transients in the flow model tend to influence the capture zone geometry over time. Thus, transient analyses of well capture zones are superior to the steady-state analogs for all practical cases with time-varying flow parameters. Energy gradients drive groundwater flow like any other natural phenomena. Along with the evolving capture zone, energy transformations within the model domain were also, therefore, assessed to portray the state of the system with time. The energy components, in the form of frictional dissipation and change in internal energy, were estimated at all time steps beside delineating the capture zones. This paper numerically models a two-dimensional homogeneous isotropic confined aquifer and thereby delineating the capture zones by subsequent examination of the energies within. The energy approach facilitated the identification of areas having pronounced transient behavior compared to the entire region within the capture zone and model domain. The current study reveals that there was an unusual increase in the internal energy term for two time periods of the entire cycle investigated and highlighted the compressibility effects of the system. This has been correlated to the change in the distribution of capture fraction values within the capture zones of those specific time periods. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.