I always thought 1kg = 1L water

Anthony88: If I'm not mistaken, because water's density changes with temperature, 1L of water at 99°C would have a different mass than 1L of water at 1°C. Granted, if that were the only consideration, they could say "1KG = the mass of 1L of water at 30°C" or something like that, but then there are probably different variables like what is in the water... It's all over my head.

A Liter of water at standard temperature and pressure weighs a kilogram. We now know STP is also subject to minuscule fluctuations, and since it's the derived measurement, the Kilogram being the base, it's a bad idea to convert backward.

Yes, the specific gravity of liquids can vary, that's why we use hydrometers to measure the state of charge of battery electrolyte. So water with gases and minerals dissolved in it have a different SG than pure H2O. Water expands when heated and shrinks when cooled, until just above its freezing point where it expands again. So maybe they should use a cubic block of ice made from pure water and measures 100MM per edge? But then ice sublimes, so maybe that's not such a good idea after all? For my needs, the old way suits me just fine.
Randy

The new definition does not make sense. How can it be re-defined by using a 1-kg mass as part of the instrument? It is similar to making the definition of a word by using the word in the definition.

Um doesn't the force needed to suspend/balance a given mass relate to the local gravitational field? (and if the gravitational field changes, then the force required to balance/suspend changes) How is this a universal constant?

Don’t forget weight and mass are two different things. My mass remains the same if I were to walk on the moon but my weight (think force and measured in Newtons) is different depending on my distance from earth.

I offer $5.01 for the existing 1 kg prototype in France. The original, not any of the "copies" floating around.

#Grunchy, I’m offering $10 and I don’t want any fingerprints. And no Amazon drone deliveries - I don’t want this thing gaussed by batteries and constantly leaning north. $15 max and I’m out.

You can't use water as a reference for mass because the composition of water varies from place to place. 1 Liter of water at 20 degrees Celcius at 1 standard Earth atmosphere is more massive than the same on Earth (although it is lighter because of lesser local gravity) Martian water has a higher deuterium content than Earth water so it is heavier. To make water as a standard one would have to make it absolutely Deuterium and Tritium free and only use the most stable isotope of Oxygen too.