Is there any reason to use cold water over hot water for boiling?

Question

I was always told that boiling cold water in a pot is better for you then boiling warm or hot water (from the sink).

Is there any truth to this statement?

Answer 1

Yes, but not for any reason related to nutrition or ease-of-boiling. Older home plumbing systems may use lead solder, and lead is a neurotoxin which is particularly harmful to children. Hot water dissolves lead more readily and stays in your home's plumbing system far longer, so it may end up with much more dissolved lead than cold water. The EPA states:

How can I reduce lead in drinking water at home?

Flush your pipes before drinking, and only use cold water for consumption. The more time water has been sitting in your home's pipes, the more lead it may contain. Anytime the water in a particular faucet has not been used for six hours or longer, "flush" your cold-water pipes by running the water until it becomes as cold as it will get. This could take as little as five to thirty seconds if there has been recent heavy water use such as showering or toilet flushing. Otherwise, it could take two minutes or longer. Your water utility will inform you if longer flushing times are needed to respond to local conditions.

Use only water from the cold-water tap for drinking, cooking, and especially for making baby formula. Hot water is likely to contain higher levels of lead. The two actions recommended above are very important to the health of your family. They will probably be effective in reducing lead levels because most of the lead in household water usually comes from the plumbing in your house, not from the local water supply.

Answer 2

I had heard that cold water from the tap contains less minerals and other contaminants. The only source I found refers to lead contamination, which should be quite rare. http://www.cpsc.gov/CPSCPUB/PUBS/5056.html

If your drinking water is contaminated with lead, or you suspect that it may be, EPA recommends two immediate steps:

When the water in a particular faucet has not been used for six hours or longer, "flush" your cold water pipes by running the water until it becomes as cold as it will get.

Use only water from the cold water tap for drinking, cooking, and especially for making baby formula. Hot water is likely to contain higher levels of lead.

Answer 3

Warm tap water might contain small amounts of lead from old pipes and should be avoided according to the following sources:

fitsugar.com: Healthy Cooking Tip: Start With Cold Water

Hot water is much more likely to leach the heavy metal from your plumbing pipes. Using lead to solder pipes wasn't banned until 1986, and unfortunately brass plumbing parts might contain a bit of lead as well. Plumbing parts legally considered lead-free today may contain up to eight percent lead. This means your chances of having lead-free plumbing are slim.

This article quotes the following recommendations by EPA (the US Environmental Protection Agency): Actions You Can Take To Reduce Lead In Drinking Water

Only Use Cold Water for Consumption
Use only water from the cold-water tap for drinking, cooking, and especially for making baby formula. Hot water is likely to contain higher levels of lead.The two actions recommended above are very important to the health of your family. They will probably be effective in reducing lead levels because most of the lead in household water usually comes from the plumbing in your house, not from the local water supply.

This was also published by the New York Times The Claim: Never Drink Hot Water From the Tap:

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.
[..]
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. It also warns that boiling water does not remove lead but can actually increase its concentration. More information is at www.epa.gov/lead or (800) 424-5323 (LEAD).

Note that this is USA specific. Other countries might have banned lead soldered pipes much earlier or replaced such already.

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See also this related question on Cooking.SE: Is hot tap water safe for cooking?.