Are you taking Vitamin B12?
I agree with R.
I think most of those zero calorie water things are loaded with B vitamin.
The B vitamin most likely to cause the neon yellow color in your urine is vitamin B2, not B12. B2 is also known as riboflavin. MOST B vitamins are water soluble, and this is the case with vitamin B2, or riboflavin. The neon color is not something you need to be concerned with. I have this color almost all the time, as I am told to take more of the riboflavin to help prevent migraines.
Really, with those vitamin and energy drinks the main things to be concerned with are the same as with soda or ready made sweetened tea drinks: You still need to be concerned with the amount of caffeine and sugar/ high fructose corn syrup that you consume.
Most doctors and the laboratories that they use know about this cause of neon colored urine. So, really, unless you're NOT drinking these drinks with all those B vitamins in them, there is no reason to be concerned with the neon yellow urine. This is normal with these water soluble vitamins.
I think they nailed it. Vitamin rich drinks. I bet you are really pounding them...4 or 5 a day? Tap water in a cup id your best bet.