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In "Why you shouldn't use hot tap water for drinking or cooking" | Vancouver Sun, 2010, Chad Skelton did some research and got the following from a quality expert at his water company in Vancover.
"Generally I would say itÕs better to use cold water and heat it up because the cold water is fresher from the supply. Hot water can reside for extended periods either in a hot water tank or in the hot water recirculation system in the case of an apartment building or condominium. Since [Metro Vancouver] water is soft it leaches metals (copper is mainly at play here) from plumbing systems and this is especially relevant in buildings with recirculating loops. [Metro's] Water Treatment Program includes pH and alkalinity adjustment aimed at reducing the level of copper leaching. Also, weÕve heard anecdotally that some buildings may actually treat their hot water to reduce the leaching. IÕm not aware of any instances where chemical contamination has occurred from the water sitting in the hot water system but since water does contain a small amount of sediment, it has been known to accumulate in hot water tanks and most tank manufacturers recommend periodic flushing of the sediment from the tank by opening the valve at the bottom. ItÕs likely that not many home owners follow this advice."

A 2008 article in the NY Times "Lead Contamination - Tap Water" - Medicine and Health , Anahad O'Connor, says
"Lead is rarely found in source water, but can enter it through corroded plumbing. The Environmental Protection Agency says that older homes are more likely to have lead pipes and fixtures, but that even newer plumbing advertised as Ōlead-freeĶ can still contain as much as 8 percent lead. A study published in The Journal of Environmental Health in 2002 found that tap water represented 14 to 20 percent of total lead exposure."

Scientists emphasize that the risk is small. But to minimize it, the E.P.A. says cold tap water should always be used for preparing baby formula, cooking and drinking.

Lead Contamination - Tap Water - Medicine and Health - New York Times, 2008
Why you shouldn't use hot tap water for drinking or cooking | Vancouver Sun, 2010

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last updated 1 June 2014