How to use our Folia Filters

Step 1: Create a folded cone from a circle

  • Fold the round piece of filter paper in half and form a crease. Then, fold it again in half and crease to produce a quarter circle.
  • One outer layer of paper is separated from the other three (not two and two!) and the opening is made wider by squeezing slightly together at the creases.
  • TIP: The filter does not work as a water filter if it is cut and taped or glued  closed.  It is very difficult to get a water tight seal, and can leave small holes in the filter seam, leading to irregular antimicrobial performance.

Step 2: Place the folded cone into the Keystone Funnel

  • To use, the conical shaped piece of filter paper can be placed in any funnel, but we recommend using our Keystone Funnel, which has been designed to fit the folded cone exactly.
  • After placing the paper cone in the funnel, it stays in place best by slightly wetting the filter paper with water.
  • Snap the lid of the funnel onto the large round funnel opening.  Be sure to twist the lid into place.

Step 3: Attach the base of Keystone Funnel to the empty (bottom) bottle


  • The Keystone Funnel has been originally designed to as a connector to hold the filter paper in place between two bottles.
  • Put on the Keystone Funnel's plastic thread cap, and screw the base (narrower end) of the Keystone Funnel onto a clean, empty bottle or other water container.

Step 4: Attach the lid of the Keystone Funnel to the full (top) bottle

  • Turn the empty bottle and Keystone Funnel over and screw the Keystone Funnel's lid onto the bottle of dirty water.



Step 5: Do "The Flip"

In one fluid motion, quickly flip the whole system over to initiate gravity-based filtration. It will take around 15-20 minutes to filter 2 liters of water. When filtration is complete, remove the Keystone Funnel and drink safe water.

TIP: Do not hold the bottles in parallel to the ground for very long during the flip.  This can cause water leakage from the funnel and result in a big mess!