> Contamination of drinking water The PEX EIR found that methyl tertiary-butyl ether (MTBE) and tert-Butyl alcohol can leach from PEX in amounts that exceed taste, odor and health guidelines set by the State of California for drinking water. The PEX EIR found that PEX pipes can initially leach as much as 290 ppb of MTBE. The California Department of Public Health and the California Office of Health Hazard Assessment have established a drinking water taste and odor standard of 5 ppb for MTBE and a drinking water public health goal and maximum contaminant level of 13 ppb. One of the key issues for the California State Pipe Trades Council was the recognition that construction workers are often the first to consume water from newly installed pipes. Because the levels of MTBE contamination from PEX pipe are highest during the first month of use, workers were at risk of repeated exposure to drinking water contaminated with MTBE at levels exceeding public health goals as they moved from job site to job site. The PEX EIR found that, unlike copper pipe, outside contaminants such as pesticides, oil, gasoline, and benzene can permeate through PEX pipe into drinking water. Several studies and articles comparing potable water pipe materials, including variants of PEX, polybutylene, polypropylene, CPVC, copper and steel, have found that PEX, at least initially, displayed the strongest biofilm formation and the strongest promotion of the growth of Legionella bacteria.