Considering there’s water in the Soylent 2.0 that you’re drinking (and assuming you’re drinking at least three or four bottles a day) plus the fact that you’re drinking four glass of water in addition to that? I would say you’re probably fine regarding water intake. The notion that humans need to consume eight glasses of water in a day is not based on science at all. It’s just a thing people say… like “We only use 10% of our brains.” That one’s not true either
I’ve been on 100% Soylent 2.0 since it was released, only eating solid food when I dine out (2 maybe 3 times a week at most and only on the weekends). I haven’t experienced any abnormalities.
My guess would be that it could be low sodium levels, as others have pointed out. The amount of sodium a person needs could probably vary greatly depending on the individual… with things like BMI, metabolism, amount of physical activity, etc. etc. all factoring in.