About 97% of the water on Earth is salty. Of the 2.5% that is fresh, nearly 70% is locked in ice and about 30% is hidden underground. Lakes and rivers, where we draw much of our water, hold only about 0.3% of all fresh water. All told, less than 1% of the planet's water is both fresh and readily accessible.
On 27 August 1883, the eruption of the Indonesian volcano Krakatoa was heard as far away as Rodrigues Island, nearly 4,800 km away. Its pressure wave was picked up by barometers worldwide and circled the globe several times. The tsunamis that followed killed more than 36,000 people.
The deepest known point in the ocean, Challenger Deep, lies roughly 10,900 m below the Pacific surface. Drop Everest in and its summit would still sit about 2 km underwater. Down there, the pressure is more than 1,000 times what you feel at sea level, roughly a tonne pressing on every square centimetre.