When thinking about energy conservation, I’ve pondered whether it’s more energy efficient to run the kitchen tap for a bit to get HOT water, or just to heat cold water up on the stove.
The answer appears to be: worrying about that is moot. From the New York Times:
The reason is that hot water dissolves contaminants more quickly than cold water, and many pipes in homes contain lead that can leach into water. And lead can damage the brain and nervous system, especially in young children.
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 “lead-free” 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.