From a properly functioning A/C unit, the condensed water is pretty similar to rain water. Of course it's possible that the A/C unit is contaminating the water, e.g. with bacteria if the water accumulates in the unit before draining. Take a sample and let it set in a clear glass inside for a day or two and see it looks/smells pure. Or have it analyzed. I assume you're asking because you live somewhere with drought - if water were cheap and plentiful, I probably wouldn't chance anything with my grow...