When the Titanic sank on the 14th of April, 1916, the people aboard the ship jumped into water that was below 0° Celsius.
Although the exact temperature of the Atlantic couldn't be determined, it is estimated to have been -2° Celsius, which means you have a few minutes before the cold overpowers your body and you fall into hypothermia, before eventually dying.
Charles Joughin, a chef on RMS Titanic was arguably the last person aboard the ship when it sank into the cold waters of the North Atlantic ocean and once it all came crashing down into the water, the very drunk baker managed to survive 3 hours before finding a lifeboat.
Joughin had been on the high seas since he was 11 after following the footsteps of two of his brothers, who had both joined the Royal Navy. This had led to him being on that ill-fated ship all those years ago.
As you remember from the film, by this time, icy cold water was rushing into everything on the ship. Now any average person would have panicked. But not Joughin. The baker quietly walked into his room and reportedly started having brandy, quite a bit of it, if you remember the film.
He is then said to have given his lifeboat to others, saving their lives in the process. By this time, the ship was out of lifeboats and so he practically became the very last person to get off the ship.
If you remember the film, just before the ship broke in half, Jack and Rose were hanging from the railings, you would notice that they had managed to pull another man onto the railing.
That last part actually happened. Not the Jack and Rose part. But when Joughin heard that the ship was about to snap in half, he immediately made his way to the stern of the ship and clung to the railing.
Titanic's second officer Charles Lighttoller describes falling into the icy cold water of The Atlantic to be the same as 'a thousand knives being driven into one’s body'.
The shock alone killed many people, while many others fell to hypothermia almost immediately.
But Joughin, calm as ever swam through it all, and kept paddling for hours, till he found a lifeboat at dawn. However, it had no space, even to stand.
However, some moments later he spotted another lifeboat with room and was finally pulled out of the Atlantic.
Joughin lived and later joined the Merchant Navy during World War I. He passed away in 1956, at the ripe old age of 78. His character was later portrayed in the James Cameron's Titanic.