由于水务公司在其管理过程中纳入了综合资源规划，因此有必要纳入外部性的概念。随着节水项目成本和效益评估方法的发展，这一点尤为重要。本文旨在介绍与外部性相关的问题，包括外部性的定义、外部性内部化的方法，以及估算外部性成本和收益的方法。虽然大多数关于外部性的讨论都强调对环境的负面影响，但本文将阐述与节水相关的正外部性和负外部性。包括18篇参考文献。

As water utilities incorporate integrated resource planning in their management processes, it it necessary to incorporate the concept of externalities. This is particularly important as methods evolve of evaluating the costs and benefits of water conservation programs. The purpose of this article is to provide an introduction to the issues surrounding externalities, including their definition, methods of internalizing externalities, and a survey of ways to estimate costs and benefits of externalities. Although most discussions of externalities emphasize negative effects on the environment, this article will illustrate both positive and negative externalities associated with practicing water conservation. Includes 18 references.