tion of processes for coagulation with ferric chloride or lime (especially high-lime treatment), granular media filtration, membrane filtration, reverse osmosis, air stripping, ion exchange, advanced oxidation, and high level disinfection with free chlorine, ozone, UV light, and other means.

Training should include courses on the various microbial pathogens and indicators. Operators should be familiar with many of the most important microbial organisms, the diseases they cause, the symptoms of those diseases, the likely density of the organisms in wastewater, and the relative effectiveness of the various treatment processes in removing each one. Operators should also be generally familiar with the procedures for isolating these organisms from drinking water as well as some of strengths and weaknesses of the various analytic techniques.

The safe, reliable operation of a potable reuse water system depends both on well-designed treatment trains that provide redundant safety measures, or "multiple barriers," and on monitoring efforts designed to detect variations in system operation as well as any signs of contaminant breakthrough in the system. Such duplicative barriers and monitoring efforts are essential to reducing, detecting, and mitigating any weaknesses or lapses in the system's safety performance.

To provide these margins of safety, the committee recommends the following:

• Potable water reuse systems should employ independent multiple barriers to contaminants, and each barrier should be examined separately for its efficacy for removal of each contaminant. Further, the cumulative capability of all barriers to accomplish removal should be evaluated, and this evaluation should consider the levels of the contaminant in the source water, the expected health effect associated with the contaminant, the goals that have been set for the potable supply, and any additional factors of safety.
• The multiple barriers for microbiological contaminants should be more robust than those for many other forms of contamination, due to the acute danger such contaminants pose at high doses even for short time periods. Where reclaimed water is used to augment natural supplies or where source water cannot be protected from upstream discharges of water with impaired quality, the importance of the barriers at the water treatment plant or wastewater reclamation plant is correspondingly increased.
• Because the performance of wastewater treatment processes may vary considerably from time to time, such systems should employ