When left unattended, natural resources tend to inch toward depletion, overuse, spoilage, or pollution. Common pastures get overgrazed; lakes are overfished; rivers are polluted, and so on. In the case of water, some may wonder how overuse or depletion is possible, as water is a renewable natural resource. In spite of this, depletion and overuse can occur in a practical sense and on a local level. The reasons for this overuse are often related to the "tragedy of the commons," a situation where individual users of a common resource pursue their self-interest without coordination and thus behave collectively in ways that are not optimal for the resource as a whole. This note explores the concept of the tragedy of the commons in relation to water, considering especially the implications of water's status as an unprotected open-access resource.