Is hot tap water safe for cooking?

  • Is hot tap water safe for cooking? jontyc

    I'll typically bring hot water from the tap to the boil instead of waiting longer for cold water. This hot water comes from water heater with a large storage tank. Is this considered safe?

    For example, are heater storage tanks known for festering nasties not killed by boiling? Is different piping used for hot water or different soldering on pipe fittings? Do hot pipes cooling down go through a temperature more conducive to bacteria growth?

  • Unless your hot water tank is very close to your hot water tap, this is a very energy inefficient. As Jefromi notes it would be faster to boil water in a electric kettle first, and then pour it into the pan. Put the pan on the heat at the same time if you are really in a hurry

    Hot water systems are normally hot enough (above 55°C, 130°F) to keep water borne nasties at bay, plus if you are on town supply water it will be chlorinated etc

    Normally on the first few meters of hot water pipe are copper, then it switched to normal crimped plastic plumbing. This will vary depending on your local building codes

    The rate at which pipes lose their heat would ensure it never sits in the danger area for long, not that I think this is a big issue for clean plain water

    In general, modern copper pipes are not soldered, they are crimped using special hand tools

    Old or non-renovated houses may still be 100% copper pipes that have been soldered. This poses no extra safety risks with just clean water in the pipes

  • May not be a direct answer, but too long to be a comment. In short, there is really no need to use hot tap water for cooking.

    Unless the temperature of your hot tap water is near boiling point high, it does not necessarily boil significantly faster than room temperature or cold water. I am not saying hot water does not boil faster than cold water, just not to a meaningful extend.

    See the following excerpt from Scientific America

    "..cold water will be absorbing heat faster while it is still cold; once it gets up to the temperature of hot water, the heating rate slows down and from there it takes just as long to bring it to a boil as the water that was hot to begin with.."

    The reverse is even more interesting: hot water may freeze faster than warm water:

    ..It all depends on how fast the cooling occurs, and it turns out that hot water will not freeze before cold water but will freeze before lukewarm water. Water at 100 degrees C, for example, will freeze before water warmer than 60 degrees C but not before water cooler than 60 degrees C..

    In addition to heath and energy/money concern, I do not see any reason to use hot tap water for cooking.

water food-safety
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