One easy thing to change if immersion is important without much change to balance would be to remove the ability to drink from water directly. Lake water is simply toxic.
Because if I understand many of you correctly the discrepancy that stands out among all the other discrepancies that were always and will always be there is that you can drink lake water but not store it and drink it later for the same effect.
Balance would be affected by having no emergency source of drinking. But you could simply incorporate the damage done by drinking lake water into the debuff of being thirsty. I.e. when you are under 10% water you simply get the damage as if you drank one water from a lake. And this would be repeated in about the same time that one lake water drink would last you.