I have a trane unit in the attic that is for the

The water is condensate, which is produced by the air conditioner (this normal), The hole you are refering to shoule be connected to a drain, and should have a "p" trap installed to allow proper drainage and prevent sewer smells from backing up into the air handler. The pan underneath it should be a secondary catch incase there is a problem with the primary drain (the hole from the unit). the secondary catch should also be equipped with either a drain to allow the water to escape, or a moisture sensor to shut-down the air conditioner, and alert the homeowner to the problem, by way of the house getting warmer. The fact that you describe it as simply a hole draining into the secondary pan tells me that this unit is not installed properly. I suggest calling the installing contractor to remedy the situation, before costly ceiling repairs are required.