IMO, a Water Fast isn't enough to get rid of Candida. Well, I guess that depends on how bad your Candida is. It's probably left it in a pretty weak state. You'll need to hit it hard with antifungals to knock it back into submission.
I completed a 32 day juice fast last year. The last two weeks of the fast was nothing but green juice (no fruit). At the end of the fast I started doing ACV Enemas. I was blown away by how much Candida was coming out of me after not eating anything for over 30 days! So it would appear that the Candida didn't have any problem hanging out while I was fasting.
Nothing wrong with fasting, but now you really need to hit it hard with Coconut Oil, Oregano Oil, etc.
BTW, good job going 21 days on water! I'm just now considering doing my first three day water fast.