Water Kefir Grains ( also known as Tibicos in Mexico, Japanese water crystals and California bees) are a SCOBY – a symbiotic colony of bacteria and yeasts, held together by a polysaccharide biofilm matrix created by the bacteria. The grains can maintain a stable culture by using carbohydrates ( ostensibly sugary liquids) to produce lactic acid, ethanol and CO2 which carbonates the drink. They seem to have had a have a much wider world distribution that milk kefir grains, which are known to originate from the Caucasus region. Water Kefir Grains have been used in Mexico for many years in the production of a fermented pineapple drink called tepache. Wikipedia says that the grains form on the pads of the Opuntia cactus (from Mexico) as hard granules that can be reconstituted in a sugar-water solution as propagating water kefir grains.
Water Kefir Grains are found all over the world and cutures are never exactly the same, but typically containing species from Lactobacillus, Streptococcus, Pediococcus and Leuconostoc bacteria and Saccharomyces, Candida and Kloeckera yeasts. They are thought to be a relation of the ginger beer plant that some of us may remember from our youth.