Permeability in fluid mechanics and the earth sciences (commonly symbolised k). It is the measure of the ability of a porous material (often, a rock or unconsolidated material) to allow fluids (e.g. water) to pass through it.
Perspectives are different frameworks from which to explore the knowledge around sustainable sanitation and water management. Perspectives are like filters: they compile and structure the information that relate to a given focus theme, region or context. This allows you to quickly navigate to the content of your particular interest while promoting the holistic understanding of sustainable sanitation and water management.