A Glowing Bath! by Haley Barber A Glowing Bath!Tonic water makes kids bath water glow a COOL blue. It is 100% safe. We used one 2 liter and our water glowed insanely bright. Just add the tonic right to the tub as you are filling the bath. And turn on the black light! No harmful chemicals. No highlighters. Just a safe edible beverage found at almost any grocery store. You can use regular or diet variety. Neither will make the water sticky. It will feel exactly like plain old water only it GLOWS!