My cooking style involves putting a bunch of ingredients (e.g. chicken, rice, mushrooms, tomatoes) in a pot, adding water and seasoning, turning on the heat, and coming back half an hour later.  (Don't steal my techniques please.)  The problem is that this [highly scientific] method is sometimes inaccurate in the amount of water that remains in the dish after half an hour.  If the water is running low, I can just add more, problem solved.  But what can I do if there is too much water?  It's true that I can try to learn from my mistakes and add less water next time.  However, is there a way to save the dish?  I know I can just remove the top, turn up the heat, and let the extra water boil off, but sometimes that will overcook everything to a mush.  Is there anything I can add that absorbs the water?  Kind of like rice, but maybe faster? 
This sounds just like my cooking technique, and I have come up with a few ways to recover from overwatering.  Always lowball the amount of water  Like you said, you can always add water later. But if you're not watching the dish, you don't want the water to run out and burn.  Corn starch  Corn starch is a good way to thicken up the water into something more saucy. This is my preferred method if the extra water actually has flavor, because it adds a nice sauciness to the dish. Make a corn starch 'slurry' by mixing  cold water and some corn starch, then add that to the hot dish that still cooking. You want to cook the dish for a few minutes after adding corn starch to let it thicken and cook out the raw flour flavor. You'll have to adjust the amount of corn starch depending on how much water there is, but a little goes a long way, its WAY more absorbent than flour.  Remove the lid and stir occasionally  This is the easy way, but it takes a while and sometime you can cook your dish in to mush. This lets excess water evaporate, and stirring just helps that a little. 