I don't see how that could be true. the spores would need water to germinate...maybe it's the chlorine in the tap water you're using??A big misconception of PM is that water helps it spread but water actually kills the spores! I've sprayed my plants that had signs of PM caused from a root aphids attack with plain tap water ......it's been working just as good or better than the GreenCure I'd been using!!
Just make sure you do this with the lights on and be mindful that soaking the buds too much may potentially lead to bud mold or some other kind of pathogen(s).