patsy--- I 've had the same kind of headache and have been on magnesium when they occur. It was hard for me to tell if it was the water or the magnesium, but I felt kind of "funny" ---it's funny that you mention this because i had the thought that it felt like i was "water-logged" .....i dunno.....i don't think the water causes the headaches though, esp. if you're not taking several gallons,....i think it's the magnesium. what form are you taking? if it's oxide form, or grocery store brand, it could be the oxide form is too powerful for you, or that there are added ingredients that are affecting you. i'm still trying to decide what to do about magnesium myself. sorry i'm not much help.