If the flow of water through the ground coffee is not homogeneous, there will be grains that are not enough exposed to the water and grains that are exposed too much to the water. Again, the result is waste. The question of how to optimize the coffee percolator and the grinding of the coffee beans with respect to waste is a question that belongs to the physics of porous media. Flow in porous media enters our daily lives in surprisingly many ways. Blood flow in the body is an example, and so is irrigation of plants.
Oil production is yet another example, as is the spread of contaminants in soil.
Flow in porous media as a research field is extremely rich. Even though many have worked on problems within this field through the years, hosts of problems remain. Perhaps the most outstanding one is the following one. On a scale where the individual pores enter the description. This is the scale at which most of the work has been done in the framework of basic physics research.