A mixture of flour and water at room temperature is a very hospitable growth medium for many bacteria, yeasts, and molds; and indefinitely is a long time.... Even if you are extremely vigilant when it comes to kitchen hygiene, the mixture will eventually start to grow some form of microbes. This process could take a week or more to become obvious.
If you use the batch up within a week or so it is unlikely to cause any problems. For longer storage you should refrigerate the dough and/or add salt (in the proportional amount you would use for bread). If it develops an off smell or visible mold you are better off throwing it away.
Keep in mind that hydrating flour, especially whole grain flours, activates amylase enzymes that break down starches into simple sugars. This process, called autolysis, improves browning and flavor, but if allowed to go on too long it leads to a gummy crumb or poor overall structure.