Holy water has a central role in shaping the understanding and beliefs of holiness in general, but how does holy water work, and what defines holy water? By analyzing holy water in three different religious traditions—Christianity in Northern Europe, Ethiopian Orthodox Christianity, and Hinduism—the aim is to discuss the metaphysical essence of water in human understanding and ideas of holiness embodied in water. On the one hand, holy water represents purity and has to be protected from defilement, but on the other hand, many holy rivers are severely polluted. This seeming paradox will be analyzed by focusing on actual beliefs and uses of holy water in ritual and religious practices. Holy water transmits purity and holiness, but it also transfers, transports, and transforms impurities. In the process of obtaining spiritual purity, devotees may pollute the holy because holy water is believed to have a divine agency. By comparing ritual practices and beliefs in three distinct religious traditions in Europe, Africa, and Asia, it is possible to enhance the understanding of the ways holiness and holy water are perceived to work in cultural-specific religious worldviews based on essential capacities of water cross-culturally. This directs the attention to the structuring mechanisms at work because water is conceptualized and used as holy in remarkably similar ways in many religions.