I drink about 5 litres of water a day, and my head & face sweats are no different to when I was drinking between 8 & 10 coffees a day or just a litre of water.
So I gave up coffee and now only drink water, cos of one of my meds I am always thirsty so drink to ease that x

I don't know. But this is something I've been wondering about. If you drink more, will you just sweat more out or do you need to replace what you've lost? It's a bit of a conundrum.