3. Build the Filtration Layers

The order and preparation of each layer is essential for an effective filter.

Bottom Layer – Cotton:
Place a layer of cotton directly above the cap holes. This works as the final guard, catching fine particles before water exits the filter. Press it down gently—firm enough to stay in place but loose enough to let water pass.

Second Layer – Charcoal:
Boil your charcoal beforehand to remove dust, impurities, and any harmful substances. Then crush it into small chunks—not powdery, but small enough to increase surface area. Charcoal absorbs impurities, odors, and chemicals from the water.

Third Layer – Clean Sand:
Add a layer of fine, clean sand. This traps smaller particles and helps water flow evenly through the filter.

Fourth Layer – Additional Charcoal:
Add another layer of charcoal to increase purification efficiency and provide an extra safety barrier.

Fifth Layer – Top Sand Layer:
Place another layer of clean sand on top. This prevents charcoal from shifting and acts as the first filter for finer debris.

Sixth Layer – Gravel or Small Pebbles:
Top everything with a layer of clean gravel. This blocks leaves, twigs, and larger debris from entering the filter, while helping to evenly distribute the water flow over the sand layer.