A project to demonstrate the feasibility and safety of recycling water under operating conditions was performed in the Hemet-San Jacinto Valley of the State of California. Since the Valley is a closed basin, and is dependent in part upon imported water, it was felt that recycling of the water would ultimately lead to a reduction in the salt input and resultant degradation of the existing underground reservoir. The project added considerable knowledge and experience to the technology of intermittent wastewater percolation and associated monitoring techniques. A novel feature of the project was the employment of highly sensitive temperature probes to trace the lateral migration of the recharged water, much of which appears to be escaping as shallow underflow to the San Jacinto River and hence not reaching the deep groundwater table.