Understanding water flow through soils and other porous materials is critical for a wide range of applications, including agricultural irrigation, groundwater management, and environmental remediation. When water infiltrates into unsaturated soil, its behavior may deviate from what predicted by classical models: instead of a smooth, monotonic front, phenomena like saturation overshoot and fingering instabilities can emerge. Our research addresses these complex behaviors by developing a more comprehensive mathematical framework based on mixture theory, which goes beyond the conventional overdamping assumptions underlying Darcy’s law. To implement this, we have developed a new computational solver within the OpenFOAM framework, using a finite volume method and the PIMPLE algorithm. The solver will be extended to handle more complex multiphase flow scenarios, extending its applicability to diverse environmental and engineering problems.