pizzagrande,
As zalicious noted, baker's percents are part of a weight-based system, so to calculate the amount of water, by weight, you multiply the weight of flour (either in ounces or grams) by 60%. To convert the weight of water to a volume, if that is what you are after, you would have to use a tool such as the one at
http://www.unclesalmon.com/tools/food.php (left hand side of the page).
Peter