We eliminated all but fabric and activated carbon due to the following reasons:
For sand & biosand filters, the biological layer of the biosand filter would die from the freezing temperatures during the winter, but moreover, sand filters wouldn’t be possible because there would be no clean water to wash the sand to filtering standards.
Ceramic filters seemed ideal in concept since it’s sustainable and easy to make, but the freezing temperatures during the winter would most likely cause cracking and leave the filter inefficient. Furthermore, we deemed backwashing and maintenance too difficult in the long run.
S. potatorum seed and moringa seed is available in Tibet and Indian regions but preparation for use requires crushing and mixing with a salt solution that needed precision that seemed too complex for our system.
We decided to use a combination of activated carbon and fabric to design our system. Although activated carbon is sustainable and effective, the locality of the material was an issue of high concern. While brainstorming for filter designs we were lucky enough to stumble upon bamboo charcoal last minute.
“Bamboo charcoal, outcome of pyrolyzing bamboo, is a sort of porous material with excellent adsorption, electromagnetic shielding, and infrared emitting capacity.” With the same adsorption properties as activated carbon, we decided to replace activated carbon with bamboo charcoal because of its locality. However, as we kept researching we found several additional benefits that made bamboo charcoal more favorable than activated carbon:
- Even if China didn’t sell already made bamboo charcoal, its production is a possibility (instructions on making kilns for heating and details on the process can be found at source 1); although not preferred because of its complexity.
- Unlike modern carbon filters, bamboo charcoal has the added benefit of a built-in team of microbes working to decompose toxic substances like trihalomethane and chlorine. 
- As bamboo is naturally anti-bacterial and anti-fungal, bamboo charcoal also possess similar properties. Bamboo charcoal also absorbs 2,4-dichloro-hydroxybenzene, a major harmful pollutant in drinking water. Bamboo charcoal also eliminates harmful substances such as surplus chlorine, chloroform. 
- Bamboo charcoal is rich in a number of minerals including potassium, magnesium, sodium, and calcium. As it filters your water, its minerals are dissolved and it enriches the water.
- Easy to use and replace. It can either sit in water at room temperature, or be boiled with water. Depending on the frequency of usage, bamboo charcoal can lasts from 3 weeks to 3 months. 
Furthermore, bamboo charcoal has benefits other than purifying water that would serve well in Tibet:
- Reduces indoor air pollution— reduces smog as it absorbs carbonic oxide, ammonia, formaldehyde, benzopyrene, nicotine, tar etc are found in smog, that is harmful to the human body. 2 Bamboo charcoal could potential assist in decreasing excessive smoke caused by cooking in kitchens.
- Recyclable—“After end of usage life, shatter bamboo charcoal into fine pieces and mix with the soil. It activates soil and revives plants, making them nice and healthy.”
- Natural— Tibetans will be more inclined to accept and use the filter because it’s in line with Buddhist beliefs.
- Widely used– Japan uses it to enhance the flavor of tea and rice.
Thus, we switched activated carbon out for bamboo charcoal and decided to add a disinfection process to our system since bamboo charcoal can filter out chlorine. We are aware that developing countries aren’t accustomed to the taste of chlorine, which is why we only decided on chlorine after we discovered bamboo charcoal and its abilities to filter out the taste.
 JIANG, Shenxue. “Training Manual of Bamboo Charcoal for Producers and Consumers.”Http://terrapreta.bioenergylists.org/. Bamboo Engineering Research Center Nanjing Forestry University, n.d. Web.
 Goodwin, Lindsey. “Bamboo Charcoal.” Bamboo Charcoal. VeeTea and Copy & Taste, 21 Apr. 2007. Web.
 “Benefits of Bamboo Charcoal.” Greenyarn LLC. N.p., n.d. Web.
 “Water Quality.” Quality Bamboo Charcoal Products. TAKETARO, n.d. Web.