What to do with seized / split chocolate?
If you're not talking about very much water getting into the bowl, then these techniques should help. 


Remove the bowl of chocolate from the heat source.
For every ounce of chocolate, add one tablespoon of one of these:   warm water, melted butter, vegetable oil, hot milk/cream.
Stir or whisk until smooth. Add a bit more liquid if needed.
Use the repaired chocolate for sauce, frosting, or a batter (like for your brownies!). It won't work well for coating candy. 


You may also want to check out this discussion on how to melt chocolate without getting it wet.