Both Swiss Water and Descamex (the company in Mexico that does Mountain Water Process) use highly filtered water in their decaffeination systems - reverse osmosis and all of that stuff. But water is only the base of the solvent they use. They include other parts of the coffee bean chemistry in the extract in order to get the caffeine to come out and the good stuff to stay in. That's part of the sciency-magic that's going on in that whole process.