They're convenient and inexpensive to obtain. The NSF (National Science Foundation) requirements are adhered to in design for this systems. Personally, I detest the flat taste of distilled ingesting water. However, not just any old yeast will make. http://3081089Em4.Wicp.vip/ambrosebromilo/gravity-water-filter2066/wiki/Feng+Shui+Cures+For+Health+And+Purification