in the Sous vide thread the manufacturer claims that “Warmer water is lighter than cooler water.”

I’m fairly certain that the statement above is not true.

According to Einstein and e=mc2, energy is neither gained or lost. To add heat to water would increase its weight and to remove heat would decrease its weight.

Does anyone have a definitive answer on if water gains or loses weight when heated?

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It weighs less, density of water decreases slightly with higher temperatures.

Warm water is less dense than cold therefore for equal volumes of warm and cold, the warm will weigh less. Note that to match the volumes one can not simply heat say a gallon of water and weigh it. The matching volumes must be produced at the test temperatures or the weight calculated using a formula I have long forgotten.

I just had this demonstrated at home. If the top element in an electric water heater goes out but the bottom element is still working, it will take longer to heat the entire tank, but it will be fairly uniformly warm after a time; the less dense warm water will rise into the colder top half. If the bottom element takes a dump and the top one is working, you'll run out of hot water in half a tank; the lower half will stay cold. Virtually no mixing.

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Per a fixed volume of Water.

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I believe there's an exception -- water reaches its maximum density around 39 degrees, and becomes LESS dense below that temperature. That's why ice floats.

Gulf Stream.

"The Gulf Stream is typically 100 kilometres (62 mi) wide and 800 metres (2,600 ft) to 1,200 metres (3,900 ft) deep. The current velocity is fastest near the surface, with the maximum speed typically about 2.5 metres per second (5.6 mph).[20] As it travels north, the warm water transported by the Gulf Stream undergoes evaporative cooling. The cooling is wind-driven: Wind moving over the water causes evaporation, cooling the water and increasing its salinity and density. When sea ice forms, salts are left out of the ice, a process known as brine exclusion.[21] These two processes produce water that is denser and colder (or, more precisely, water that is still liquid at a lower temperature). In the North Atlantic Ocean, the water becomes so dense that it begins to sink down through less salty and less dense water. (The convective action is not unlike that of a lava lamp.) This downdraft of cold, dense water becomes a part of the North Atlantic Deep Water, a southgoing stream.[22] Very little seaweed lies within the current, although seaweed lies in clusters to its east.[23]"

https://en.wikipedia.org/wiki/Gulf_Stream

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Why Do Icebergs Float? - Live Science

There are several reasons. The first is due to one of water's many amazing properties: Aside from being necessary for all life (and refreshing on hot days), water is one of the few substances that is slightly denser as a liquid than as a solid. This is why ice cubes float in water.Sep 17, 2012

Why Do Icebergs Float?

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Interesting. But liquid water at say, 34 degrees, is less dense than water at 38 degrees. Ice doesn't come into the equation at that point. It reminds me that old BMWs always gave a warning when the temperature hit 38 degrees. Do they still do that? Probably the wrong forum for that question.

As for salinity, some years back a company in Israel was developing an energy source using hypersaline water (as home to the Dead Sea, they have an excellant laboratory). They found that highly saline water would not undergo convection, and the bottom layers of saline ponds in the desert could reach extreme temperatures. They used a heat exchanger to generate electricity from the phenomenon.

Unrelated to the current thread, I know, but still interesting IMO. Water is weird stuff.

Israel's 150kw Solar Pond - Renewable Energy - MOTHER EARTH NEWS

All interesting but I think we have long ago answered link's question. Unless we can work in gun control issues or Trump/Hillary hate and start insulting each other there is little more to say.

Why you thundering blathers-kite, we haven't even had a chance for this conversation to devolve into why the lack of moral virtues among the social collectives of the left leaning Inuit population and their abuse of Federal Mandates has caused the increase of the surface temperature and hence (huff, huff, pauses for breath) is obviously a plot hatched by the "One World Order" to ensure our dependence upon their monopoly on foreign oil!

Give us a page or two before you give up!

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Obama wants to take away my squirtgun.

It's a SuperSoaker.

Not what the ladies say

Now, we're cooking with gas!

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Thank you for the replies.

The most accurate response I found was provided in the discussion below where they state that if one takes a specific amount of cold water and then seal it and then heat the sealed water the weight will increase.

However the volume will also increase with the temperature.

https://www.physicsforums.com/threads/hot-water-is-heavier-than-cold-water.614373/

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