It would come down in cost with economies of scale, and improved production techniques, and... in 20 years, it would be out of patent.

I think there is a moral dilemma when someone creates something immensely valuable, but wants to be paid for it. But... wouldn't a world in which people didn't get paid quickly become rotten? And is it any different from people needing money for life-saving surgery (because the surgeons, hospitals and suppliers all want to be paid). See also the pied piper.

Factual content: there's a camping device for purifying water with ultraviolet light http://www.steripen.com/ but it just kills things, and won't remove salt or arsenic.