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Since the level of trace metals increases upon stagnation of the water, flushing the water present in the plumbing system significantly reduces the levels of lead and copper. In that respect, flushing can be seen as an exposure control measure. A study by Gardels and Thomas (1989) showed that 60-75% of the lead leached from common kitchen faucets appears in the first 125 mL of water collected from the faucet. They further concluded that after 200-250 mL, 95% or more of the lead has normally been flushed from faucets (assuming no lead contribution from other sources upstream of the faucet). In a study on contamination of tap water by lead solders, Wong and Berrang (1976) concluded that the first 2 L of water from cold water taps should not be used for human consumption if the water has been stagnant for a day. In Canadian studies, in which the cold water tap of homes was flushed for 5 minutes, no levels of trace metals exceeded their respective Canadian drinking water guidelines (Méranger et al., 1981; Singh and Mavinic, 1991). However, flushing the cold water tap in buildings may not be sufficient to reduce the levels of lead and copper below the guidelines (Singh and Mavinic, 1991; Murphy, 1993).
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