It is very well known the basic equation of hydraulics discovered by Antoine de Chezy in 1769, which relates in a quadratic form the mean velocity of flow with the slope of energy line and the hydraulic radius, in a uniform regime. This equation has been the central axis of development of hydrometrics as science that faces the huge challenges of penetrating the knowledge of earth´s streams every time more contaminated. In virtue of that, its mathematical structure and the relationship with other related formulas have been carefully examined, despite the limitation due to constancy of velocity. Starting from chemical considerations rather than dynamic ones as was used to obtain Chezy´s relationship it is possible to establish a second equation for mean velocity of fluid – in a non uniform regime- that corresponds to averaged movement of a solute poured to stream. This equation will go to relate in an accurate way several aspects of hydraulics and mass transport, sight as a single thing, allowing a vital tool for a depth study of water contaminations. To arrive this equation it was reviewed the foundations of mass transport theory in flows, stating a time dependent nature for coefficient currently used in describing dispersion phenomena, allowing to interpret properly certain inconsistencies detected long time ago in this theory. It is presented the detailed results of application of this new approach to a small stream and a larger river in Colombia.