Last time I tried a Water Fast was about 4 years ago. My diet was awful and my preparation worse. By the end of the second day I thought I was going to die. I switched to juice and even that was very hard. Needless to say I didn't last very long. I drank a pint of beer shortly after drawing to a halt. LOL.
I didn't plan to Water Fast this time but for the last 3 months I've avoided alcohol, Sugar & my intake of processed foods has been minimal. I'm on day 16 of my 'by accident' fast and despite the usual symptoms it's been a lot easier than I would have expected.
My point is this, get your diet right beforehand and it will be a lot easier. Sugar cravings are the worst so if you've been munching on bananas your body is going to be crying out for a Sugar rush. If you do end up eating no big deal, just make the necessary sacrifices in order to make the next attempt easier.