Who gives a shit what degree water freezes at on a day to day basis? Why not what temperature jello freezes at, or hot pockets, or hamburger meat? Who picked fresh water and said “yep, this is what we are using!”? You will no doubt say “well it’s important because water is everywhere! It’s freezing point is very important!” But freshwater doesn’t make up that much of the earths surface at all compared to salt water. Why are we not using the specific point that salt water freezes at as 0? And since salinity levels vary, why not pick the average salt level and it’s freezing temperature as 0? Now you might say “that’s dumb, use non salted water since the levels of salt very so much”, but the temperature that fresh water freezes at varies based on altitude and pressure and a whole shit load of other stuff. And let’s not even get into setting the temperature of water boiling as 100 degrees. How fucked up is that that what is the telltale sign something is exactly 100 degrees varies by atmospheric pressure even a few feet apart.