Having had more than my share of CT's PET's MRI's etc. I have also been told about the water issue. When I explain the dry mouth issue to them I have never had anyone object to small sips before the scans, and when they do a contrast and a no contrast scan, a sip in-between the two prior to the injection. With PET scans you do not want to talk do too much swallowing etc right before the scan because that will actually cause a false positive in the scan. The techs are supposed to make a note if there was any speaking or conversation right before beginning the scan. Once injected be still as possible, and do as little as possible. For some people this means taking a Valium prior to scan. For me it means trying to catch a quick catnap in the recliner prior to the scan and again in the machine with my ipod on. (PET only).