I dunno how you’re drinking your water coming off of your dry fast but you’re supposed to sip it very slowly for a few hours while swishing it around your mouth. If you’re chugging it you’re gonna feel sick.
Might mean that your releasing to many toxins into your blood and body at too fast a rate to deal with or your starting the dry fast with a build up of old rotting food in your intestines and colon that is beginning to ferment and partially poison you while the body tries to get it out of you (This was common for me in the past). To clear some of the rotting food out of your colon and intestines before a dry fast you could do a 2 - 5 day juice fast before the fast or eat only watermelon for that time if you don’t have a juicer or even just juice oranges, limes and lemons by hand during that time. This has worked great for me to clear our my colon and intestines before a fast so I can go more days without feeling sick all the time