Ficuses can get a root infection that causes the roots to shrivel and ultimately cause the plant to die. It is caused by allowing the soil to go too dry. However, hopefully it is just the shock of repotting that caused it to lose its leaves. Have there been any other stresses on the tree, such as low temperatures or drafts like len said or have you moved the tree to a new location? Just hang in there, give it adequate light and humidity, and remember that it won't need as much water as it did when it had all of its leaves. It very well may bounce back, ficuses are pretty resilient, they just don't like cold or changes in location.
P.S. If you are worried about chemicals in your water, use distilled water.