Gravity-Fed 3-Stage Bio-Sand & Activated Charcoal Rainwater Filtration

Build a zero-electricity biological filtration system capable of purifying 200 gallons of roof catchment water daily to drinking standards.

Purifying Water When Electricity is Zero

Rooftop catchment water contains particulate matter, bird droppings, pollen, and airborne smog residues. A biological sand filter (Bio-Sand) cleans water through physical trapping, predation by the Biolayer (Schmutzdecke), and adsorption.

Layer Composition (Top to Bottom):

1. Standing Water Layer (5 cm): Maintains hydration for the biological active zone.
2. Schmutzdecke Biolayer (1-2 cm): Microorganisms consume incoming harmful coliform bacteria and organic pathogens.
3. Fine Filtration Sand (40 cm): Washed silica sand with effective grain size of 0.15–0.20 mm.
4. Acid-Washed Activated Coconut Carbon (15 cm): Absorbs volatile organic compounds (VOCs), pesticides, heavy metals, and eliminates sulfur odors.
5. Separating Pea Gravel & Support Gravel (10 cm): Prevents sand from washing into the outlet siphon pipe.