I don't know about kvass, but they drank twenty liters of beer in the USSR. Not immediately naturally, but within 8 - 10 hours. There were problems with alcohol, and beer is cheap but weak. We bought a lot of beer, and had a booze without leaving the toilet. I'll tell you right away for people who breathe unevenly in the USSR. Of course, there were relatively few such people. They surprised by the very way of alcoholism.
The following questions will help you understand this in your question:
Why, if you drink more than 7 liters of water, you can die?
Drinking a lot of water is harmful? Is there a lower / upper limit for the amount of water consumed per day for a person?