Ultraviolet radiation sources found many application areas in science and technology. They play an important role within several markets worldwide today. One of these markets is disinfection and photochemical purification of water which has been a growing market for many decades. At the moment low pressure mercury discharge lamps are the state of the art technology. Although they have been developed towards an impressive maturity level, they still show many drawbacks as e.g. strong temperature dependence. Therefore, this paper is dedicated to a mercury free alternative radiation source for this market, namely so called phosphor converted excimer discharge lamps. They are in the centre of present R&D activities, since they offer several advantages compared to the mercury discharge lamps such as very little temperature sensitivity, a high customisability of the emission spectrum, a large form factor, and instant full radiation power after they have been switched on. A brief description of the technology of phosphor converted excimer lamps will be sketched and furthermore their potential as a possible game changer for water disinfection and photochemical water purification market areas will be highlighted.