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Girls are notorious for heavy conditioners in the hair, fabric softener in the clothes, lotions on the hands... etc, and my guess is that any showers which actually took place were short and inadequate.I've found that guests and friends in general have absolutely no idea how easy it is to 'infect' the tub water.... and why should they. I'm always fully prepared to dump and refill anytime I have people other than my immediate family in the tub.