Success in water management requires broad agreement and coalitions. But people often seem to group themselves into communities of interests and ideology, which see complex water problems differently. Each group tends to hold different truths to be self-evident, as outlined below. These beliefs, when firmly held, do not stand up to scientific scrutiny, appear to other groups as self-serving nonsense, and hinder cooperative discussions on better solutions. The counter-productive aspects of these ideas make them dangerous to policy discussions.