Water Wetter is a surfactant (spelling?). It breaks the surface tension of water/coolant allowing it to "wet" the surfaces of metal more effectively therefore removing more heat. Read this paper for a more thorough explanation.
www.redlineoil.com/whitePaper/17.pdf .
GMP is correct. Use distilled water (no minerals) and silicate free coolant. Green coolant often (not all brands) contains silicate particles which are intended to abrasively remove cooling system build-ups of rust and scale. Silicate particles can harm the delicate aluminum surfaces inside your Gasser's cooling system. Use the KTM rad cap.