Great topic.
I was always drinking very little, some days only tea and coffee, almost no water unless I went to my dance class.
I was not very much nauseated in early preganacy, however in second trimester I was having pain the the back of my neck and migraine type of headaches daily several times, some days I even vomited from that.
Then I read up dehydration and how dangerous it is in pregnancy, especially related to preterm birth (my current scare).
So this is what is working or me so far.
I have pregnancy app on my iphone which tracks your liquids intake.
Everytime you drink a glass you tap on the glass and it counts them and tells you how many glasses you still have to drink on that day. It is set on 10 glasses per day.
This worked great for me, I didnt even realized how dehydrated I must have been before, unless you track it you would never know.
And my migraines and tiredness dissappeared, I am doing it for a week now and didnt have headaches ones, I feel much better, more vital, less tired.