As water-based creatures we inhabit a very narrow range of temperature. Water is amazing stuff, and is quite unusual in that by can be encountered in all three of its phases without resorting to laboratory conditions.
At 0 Celsius water enjoys a phase transition between solid and liquid phases. Below that, ice cools a gin and tonic, makes road surfaces treacherous, makes the hexagonal beauty of the snowflake. Above that, liquid water moves from a refreshing beverage (or a bone chilling dip), through a temperate English Channel which can be dwelt in for the time spent to swim from one side to t’other, through temperatures positively dangerous to swim hard in for any length of time, all in the space of 30 Celsius or so.
Our bodies are more than half water. The precise figure depends on your age, sex, and how much fat tissue you have. Around 60% is a reasonable estimate though. While the body is capable of spending some time in water between 0 and 50 Celsius, it strives the whole time to keep its core temperature as close as possible to 37. More than 5 Celsius either way, for any length of time, and we are in serious trouble, febrile or hypothermic.
We walk this knife edge as cold water swimmers. The body does an awesome job of shutting down peripheral blood flow in cold water, thus minimising heat loss through the surface. We feel this when our extremities go numb, when the whole of our skin screams in pain when we dive in, before receding into numbness.
The third phase of water can be seen when we boil a kettle, as steam rises. We are seeing water vapour. But water vapour is all around us anyway to a greater or lesser extent, depending on the humidity.
The universe has an enormous range of temperatures. Temperatures ‘only’ go down to minus 273 Celsius or so (-273.15 Celsius, or absolute zero). In practice, absolute zero can only be ‘approached’ in the lab, and as the temperature gets closer, strange phenomena such as superconductivity and superfluidity start occurring. The lowest temperature recorded under natural conditions was a mere -89 Celsius at Vostok in the Antarctic. There’s an awful lot further to go at the top end. Our sun has a peak temperature of approximately 5-10 million Celsius. The hottest temperature observed on earth was in the region of 56 Celsius in Death Valley California, though temperatures into the billions of Celsius can be achieved under special conditions in the lab.
Liquid water can only exist over a 100 Celsius range, at least in the normal range of pressure (note – if water has stuff dissolved in it, such as salt, freezing temperature can be depressed below 0 Celsius.). We can only swim comfortably in rather less than half of that range of temperature. Long distance swimming is only really possible in a very narrow range of about 10-35 Celsius.
There are always exceptional people in life. The ice mile is an increasingly popular goal (1 mile in water <5 Celsius). Most people like me prefer it around 15-25!