"Research in the last decade has indicated that biochar, when produced at sufficiently high temperatures, can serve in large part as a replacement for standard activated carbon filters."
https://edgecollective.io/projects/water_biochar/
"To keep water safe for home and other applications, limestone helps to alter the water’s pH level. This product is necessary for water softening, purification, and pH coagulation."
https://aquahow.com/limestone-water-filter/
Gravity fed filter concept demonstrated
