# The Reynolds Transport Theorem

Keeping track of water is done through a scientific accounting methodology known as the Reynolds transport theorem, which is used to track the flows, fluxes, and storage of water in a physical system.

$\frac{{dB}}{{dt}} = \iiint\limits_{cv} {\beta \rho d\forall } + \iint\limits_{cs} {\beta \rho v} \cdot dA$

A simpler way to express this bookkeeping is as follows: