Slow sand filtration.
https://www.emergency-wash.org/water/en/technologies/technology/slow-sand-filtration
👉🏼 PDF: https://app.box.com/s/bgvz4mr38hikp7br09htbcsnm7xuafbe _ Slow Sand Filters remove suspended solids and pathogens from water with varying levels of turbidity (or ‘muddiness’) using fine sand as the filtration medium. They are used as a final treatment step and are most applicable in the stabilisation and recovery phases of an emergency.