Whether you're doing it on purpose or not, if you're not drinking enough water, you NEED HELP to get some fluids in you. Look up severe dehydration online.
Seriously, if you have emetophobia, you will probably v* more from not drinking than you will from actually drinking. Plus, you'll also survive if you drink. Your water-drinking-nausea might very well be imaginary, i.e that you're scared and making yourself think that you're nauseous. Either way, suffering through a bit of nausea now is way better than suffering from being dehydrated and in the hospital and god knows how you'll feel then! Make sure you get enough nutrition, it's important!!!