to clarify, I normally drink 3-5 liters of water per day, but when I fast I also add apple cider vinegar and salt to a few glasses of water. Salt helps retain minerals in the body and apple cider vinegar helps autophagy.
At first I worried about what foods to eat when breaking a fast, but I quickly figured out that I could eat a normal keto/paleo meal (meat and vegetables), even after a 7-day fast. Not too much, but still a decent-sized meal. Not everyone can do that, but thankfully I can have a steak as my first post-fast meal without worrying about digestion.