  We calculate the net energy per unit time exchanged between two sets of modes
in a generic system governed by a three-wave kinetic equation. Our calculation
is based on the property of detailed energy conservation of the triadic
resonant interactions. In a first application to isotropic systems, we rederive
the standard formula for the energy flux as a particular case for adjacent
sets. We then exploit the new formalism to quantify the level of locality of
the energy transfers in the example of surface capillary waves. A second
application to anisotropic wave systems expands the currently available set of
tools to investigate magnitude and direction of the energy fluxes in these
systems. We illustrate the use of the formalism by characterizing the energy
pathways in the oceanic internal wavefield. Our proposed approach, unlike
traditional approaches, is not limited to stationarity, scale-invariance and
strict locality. In addition, we define a number $w$ that quantifies the scale
separation necessary for two sets of modes to be energetically disconnected,
with potential consequences in the interpretation of wave-turbulence
experiments. The methodology presented here provides a general, simple and
systematic approach to energy fluxes in wave turbulence.
