yes, nausea is good. Well, the evidence is that lots of water is needed to produce and protect the placenta and amniotic fluid. If you're not getting enough, they could become dehydrated too, and not sdo their work properly. In this heat too, you need it even more.
The problem is, a lot of drinks are not actually counted as "drinks" in pg, cos they have so much caffeine or sugar or whatever in them, so drinking pure water is the only way to know for sure that you have had enough hydration.
If you are not having a text-book pregnancy (ie any amount of spotting, for example), you just have to make sure you are properly hydrated. It can only do good.
Just dont start drinking 8 litres or whatever - even too much water can do you harm...!
My MW told me to buy 2 litre bottles of water, and drink one throughout the day, so that I knew for sure I had had the correct amount each day.
Basically, I made sure I drank that amount of pure water, and I also drank juice and milk at other times.