selection process prioritizes sites by the likelihood of finding high lead concentrations which could impact people. Building codes and building records may be used to estimate the types of plumbing and solders at various buildings. Residential buildings are preferred over commercial, for sampling. Only taps from which water is consumed are tested. The age of plumbing is taken into account, as older piping may reach an equilibrium with the water. Unique regulatory approach Because the source of lead and copper is generally the customer-owned piping rather than any part of the water supplier's plumbing, equipment, or even the original source of water, the Lead and Copper Rule is quite unlike any of the other provisions of the National Primary Drinking Water Regulations. To some extent, the water supplier is made responsible for the quality of water sampled at pipes and locations completely out of the supplier's control. The most unusual features of the rule follow from this difference. While MCLs are risk-based standards, and the code requires the water supplier take various actions based on the MCL, the Lead and Copper Rule regulates the level of contamination at the customers' taps based on "action levels." The rule does not define an MCL for lead or copper. This approach allows some percentage of the customer taps to exceed the "action level" without the water system having to take action. Especially for the larger public water systems, having the supplier change the tendency of the water to dissolve lead in the customer plumbing may be more cost effective than having thousands of customers replace their plumbing. Also, because the source of lead and copper is the customer plumbing, lead and copper sampling is specified to be "first draw." Most other water samples are taken by the water supplier's personnel. Trained personnel using consistent procedures generally yield more reliable data. The first draw sampling procedures make water supplier sampling impractical. Rather than have a technician spend six hours in a customer's home, the water supplier may leave the sample bottles and sampling instructions with the consumer. Criticism The EPA was investigated by the Government Accountability Office (GAO) in 2003 following the discovery of higher-than-acceptable copper and lead levels in tap water in the District of Columbia. The GAO reported that the EPA had not been collecting copper and lead levels from the states, despite claims that the levels of copper and lead have