Recently, California has made large investments in wastewater recycling to replace applications that use potable water. It may be expected that the use of recycled water reduces potable water use, but such an equivalency is not assured. The addition of recycled water infrastructure in a large Californian water district creates a natural experiment where this work tests how recycled water usage affects primary potable water. This is done using econometric methods for causal inference in an observational setting that mirror a randomized control trial (RCT). From 2001 to 2014, a number of public parks were given recycled water infrastructure, while others in those regions remained exclusively on potable supply. A two-way fixed effects regression is used to produce a difference-in-differences estimate of the average treatment effect of recycled water on total and potable water usage. The results indicate that potable water usage is reduced significantly when a park is connected to the recycled water supply. The estimated rate of displacement in the study period is 81.7%, meaning each unit of recycled water use avoided 0.817 units of potable water usage, which implies the connection of parks to recycled water supply increases total water use. The analysis provides, to the best of our knowledge, the first empirical estimate of the water savings claimed by urban water recycling programs, and the first empirical estimate of displacement using quasi-experimental methods. The methodology can be utilized to evaluate the effectiveness of recycling programs around the world.

最近，加利福尼亚州在废水回收方面进行了大量投资，以取代使用饮用水的应用。可以预期使用循环水会减少饮用水的使用，但不能保证这种等效性。在加利福尼亚州的一个大型水区增加循环水基础设施创造了一个自然实验，这项工作测试循环水的使用如何影响主要饮用水。这是通过在反映随机对照试验 (RCT) 的观察环境中使用计量经济学方法进行因果推断来完成的。从 2001 年到 2014 年，一些公园获得了循环水基础设施，而这些地区的其他公园则完全依靠饮用水供应。双向固定效应回归用于对循环水对总用水量和饮用水使用量的平均处理效果进行差值估计。结果表明，当公园连接到循环水供应时，饮用水的使用量显着减少。研究期间估计的置换率为 81.7%，这意味着每单位再生水的使用避免了 0.817 单位的饮用水使用，这意味着公园与再生水供应的连接增加了总用水量。据我们所知，该分析提供了对城市水循环计划声称的节水量的第一个经验估计，以及使用准实验方法对排水量的第一个经验估计。