Then we have the linear momentum balance equation. One is the equilibrium equation for the multiphase system and then we have those for capillary water, absorbed water, water vapour and dry air.
The first one give rise to Darcy's law, the second to Fick's law, for water vapour we obtained Darcy's and Fick's law and again for dry Darcy's and Fick's law.
Finally we have the angular momentum balance equation, which says that also at microscopic level the stress tensor is symmetric.