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Inspired by What is the point of washing produce in cold water?

Multiple times I remember reading or getting advice that [ingredient X] needs to be washed in cold water before preparing and that warm water will... not precisely ruin them, but somehow make it worse.

Now, I don't remember precisely which ingredients those were... fish maybe? Or mushrooms? Could be some other vegetables too.

Anyways, this advice always has seemed suspicious to me. The difference in temperature between cold and warm water is maybe 30°C, not really enough to do anything chemically I think, and warm water is so much more pleasant for the hands... And especially for ingredients that you intend to cook right afterwards anyway, what harm can it do?

So - are there any ingredients that actually need to be washed in cold water, otherwise it negatively affects the quality of the end result? Preferably ones that are not super exotic.

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  • This doesn't exactly answer the question you asked, but you should not drink hot water from the tap. Hot or even warm water will corrode a metal pipe more quickly than cold water. Older plumbing often contains lead. Lead consumption can have serious negative consequences, especially for children. The amount of additional lead in hotter water may not be huge, but considering the risk, it's generally recommended that you not drink or cook with hot water from the tap.
    – Juhasz
    Sep 20 at 16:29
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Indeed there aren't many situations where the temperature is relevant for the food quality. I can think of only one where this would be the case.

Cold temperatures help tender leaves stay fresh longer. If you were to submerge lettuce leaves or similar greens in warm water and wash them there, you might get a less crisp salad. The difference will be very small though, usually it wouldn't be noticed.

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One of the main reasons I always use cold water is the fact that it is cleaner. It does not go through boilers and all other heating machinery, which could alter its taste or smell and then spoil your food. If your house is old enough and the water heating system has had a chance to get rusty and dirty you can actually see that the water looks different (it's not quite as clear as the cold water).

If you were to heat up the cold, clean water in a clean way (which obviously doesn't make sense, just a thought experiment), then I don't think it would make much of a difference. Having said that a friend of mine claimed that if you wash fruits in warm water it can actually open up their pores and make the dirt go inside them rather than be rinsed of, but to be honest it doesn't make a ton of sense to me.

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  • Actually... in my condo that might actually be the case! You see, we get cold tap water supplied by one company, and the heat energy by another (which is supplied by a pipe of super hot water). And then in the basement the cold water pipe gets split into two, with one half going through a heat exchanger and the other straight to the tap. So there's very little difference between the cold water and the hot - it's literally just that one was warmed up.
    – Vilx-
    Sep 19 at 13:41
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    It depends on the plumbing — and location. In the UK, for instance, hot water traditionally went through a cold water storage tank, a heater, and sometimes a hot water tank — some of which might have been open to the elements, or silted up, or whatever, so not safe to drink. Whereas cold taps in the kitchen (and sometimes bathroom) come straight from the rising main, and so are safe drinking water. (This is also why mixer taps aren't common here.) Of course, these days we're more likely to have combi boilers or other heaters providing safe hot water directly.
    – gidds
    Sep 19 at 17:54
  • If your hot water supply is not clean enough to use the water to wash your food, do you trust it to wash yourself? I would suggest to change the system to a more modern one where the hot water is of drink water quality, as is easily done these days.
    – Willeke
    Sep 19 at 20:17
  • @gidds' comment is still true for a lot of the UK. The cold header tank is covered (if modern) but not sealed. Mine certainly has some silt in it. The hot water tank might peak at 60°C, but with a timer on the hot water system can sit at a fair bit cooler for hours on end. However it is still clean enough to wash dishes you eat off. Old systems with uncovered header tanks may not be - dead vermin in them isn't unknown - so are deprecated
    – Chris H
    Sep 20 at 9:49

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