would deposit a protective coating on the pipes rather than dissolving the pipe were preferred. Corrosion indexes such as pH or Langelier Saturation Index are not necessarily representative of the lead corrosion potential in a particular water/pipe system, nor did they measure the amount of lead to which customers were exposed. In the second half of the twentieth century, concern was growing about what constituted a safe level of lead. The National Academy of Sciences conducted studies on the toxicity of lead (and other drinking water contaminants) as required by the SDWA. The academy's 1977 report suggested that the drinking water standard for lead in effect at that time may not be sufficiently protective of human health. The 1986 Safe Drinking Water Act amendments defined "lead-free" plumbing and prohibited the use of plumbing for public water supply that did not meet the new definition. The amendments also required the EPA to set standards limiting the concentration of lead in public water systems. The Reduction of Lead in Drinking Water Act, enacted in 2011, tightened the definition of "lead-free" plumbing fixtures and fittings. Adoption EPA first issued the Lead and Copper Rule on June 7, 1991. The rule required public water systems serving more than 50,000 people to survey their corrosion control systems and to obtain state approval for their systems by January 1, 1997. Smaller systems were only required to replace their pipelines if action levels were exceeded in measurements taken at the tap. EPA published the Lead and Copper Rule Minor Revisions (LCRMR) in January 2000. This rule required water suppliers to install the best available corrosion control mechanisms and to continually observe water levels, even if corrosion control was implemented. The revisions were effective April 11, 2000. Additional corrections and minor revisions were made in 2004 and 2006. A 2007 amendment added new requirements in the areas of monitoring, treatment processes, public education, customer awareness, and lead service line replacement. EPA published a white paper in 2016 discussing options for additional revisions to the rule. To implement the 2011 Reduction of Lead in Drinking Water Act, EPA published a final rule on September 1, 2020. In response to the Flint, Michigan water crisis, EPA published a final rule on January 15, 2021 addressing testing, pipe replacement and related issues. The rule mandates additional requirements for sampling tap water, corrosion control, public outreach and testing water in schools. The