You've got to get that water in or you'll get into a cycle of your lithium level being up and making you nauseous and then as it comes down you'll feel better but the cycle can progress into nausea--->vomiting--->lower lithium level--->feeling a bit better--->taking lithium---->continue cycle.

I used to get little bouts of symptoms of toxicity, enough that we treated it as a problem that had to be avoided. Not drinking enough could cause that and nothing causes nausea like lithium levels that are too high. I am literally feeling sick just remembering and writing this. Blech.