I rather like this question because it is not ‘can I dissolve my sugar in water when making chocolate?’. It implies you understand that you cannot use water in chocolate making. Fantastic. But why? Good question.
Basically because oil and water do not mix. I am going to go off of the assumption that most people know this. Oil floats on water. You have to shake your salad dressing (which contains vinegar (95% water) and oil) because it separates. There are a whole bunch of chemistry phrases and tech speak I could toss out there about the hydrophobic (water repelling) nature of oil, and how it does not hydrogen bond to the water molecules, but really that is just going to cloud the issue. Oil and water do not mix.
And what happens if you try it? Its analogy time again. Back a couple weeks, I described tempering in terms of baseballs (sugar) and bats (cocoa butter molecules) and that tempering was making a solid, locked together lattice of these. Now you want to dissolve the sugar in water. On the molecular level, you dissolve something by surrounding it by the substance you want to dissolve it in. So, to ‘dissolve’ those baseballs (sugar, if you recall), we have to surround them by….hrm, what to use in the analogy….wads of gum. Get chewing. We are going to need a lot. You need to surround those base balls with wads of gum so the balls no longer touch each other. Great. Now go stack them in a neat and tidy way with your stack of baseball bats.
What is that you say? Everything is sticking together? And it is not neat and tidy, and once you put a bat down, you can’t shift it well to make your stack align correctly? It resists those easy little shifts in alignment that were so easy when there was no gum. Yep. That’s about it. You have made chocolate mud.
That water is now the strongest player in your chocolate (way to go gum). But you only added a little? Water is amazing stuff. Hydrogen bonding. It’s why insects can walk on water. Surface tension. And that bonding just totally gets in the way of your cocoa butter moving freely around, and tempering nicely. And a little goes a LONG way. You can no longer push over your stack of balls and bats and gum. It just distorts a little. And virtually nothing you do will fix it. Congratulations – you have made seized chocolate.
I hope that gives you a better understanding of the ‘why?’ regarding water and chocolate. Why it is important to roast (or dry) your cocoa beans. Why you cannot use honey or syrup. Why you cannot use vanilla extract (you have to use scraped out vanilla beans). Why you even have to be careful using date sugar that has a high moisture content.
Finally, for more about water, there is a great FAQ about water and chocolate, that says much the same things in different ways.