I see you've already come to a decision but I thought I'd throw this in for good measure. :-) I read somewhere that the amount of water you should be drinking is proportionate to your weight, and that whatever your weight is, you half it and that's how many ounces you should drink.
For instance, my prepregnancy weight was 120 lbs. Half of 120 is 60, so I should have been drinking 60 ounces a day. Most days, I only made it to about 40-50, but it seemed to be a good formula for me, and still works even after I've gained a few pounds with this pregnancy.