Water Trivia
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This water trivia quiz has 99 free questions with answers and covers the most important substance on Earth, from its molecule to the oceans. It takes in the chemistry of H2O and why ice floats, the water cycle, the five oceans and the deepest trench, the longest rivers, the Dead Sea and its buoyancy, icebergs and rainbows, and the surprising amount of water inside the human body. Early questions suit anyone who paid attention in science class. Later ones reward people who know the world's tallest waterfall and where most of Earth's evaporation comes from. Use it for a science-class starter, a pub-quiz nature round or a family game night. Every answer has been checked against a documented source shown under the explanation.
30 of 99 questions with answers and explanations. Play the quiz
Q 01What is the chemical formula for water?
H2O
H2O overturned 2,000 years of belief that water was an element: in the 1780s Henry Cavendish burned 'inflammable air' and got water, and French chemists renamed that gas hydrogen, 'water-former'.
Q 02About what share of Earth's surface is dry land rather than water?
29%
29% is land and the rest is water; the Pacific alone covers about a third of the globe, enough room to hold every continent with space to spare.
Q 03Water is often called the 'universal' what?
Solvent
Solvent is the word because water dissolves more substances than any other liquid, which is why it is never pure in nature: wherever it flows, it carries minerals and nutrients along.
Q 04Which property of water lets insects such as pond skaters walk across a pond without sinking?
Surface tension
Surface tension arises because water molecules cling to one another more strongly than to the air above, forming a springy skin that a pond skater's legs dent without breaking.
Q 05At standard pressure, water boils at what temperature?
100 degrees C
Water boils at 100 degrees C at standard atmospheric pressure, unusually high for such a small molecule because its molecules attract one another strongly.
Q 06In the water cycle, what is the release of moisture into the air through the leaves of plants called?
Transpiration
Transpiration does more than dampen the air: as water evaporates from a leaf it tugs the next molecules up behind it, hauling water from the roots to the top of the tallest tree.
Q 07Which source supplies about 86% of the water that evaporates worldwide each year?
The ocean
The ocean supplies about 86% of global evaporation; the sun drives water off its vast surface, and most of it falls straight back as rain at sea.
Q 08Roughly what percentage of Earth's water is held in the ocean?
97%
About 97% of Earth's water is salty ocean water; only around 2.5% is fresh, and most of that is frozen in glaciers or stored underground.
Q 09Which 16th-century explorer named the Pacific after finding its waters calm?
Ferdinand Magellan
Ferdinand Magellan had battled rough seas on the way to the strait at the tip of South America; the ocean beyond seemed so calm that he called it Mar Pacífico, the peaceful sea.
Q 10The Challenger Deep, the ocean's deepest known point, lies in which Pacific trench?
The Mariana Trench
The Mariana Trench marks where the Pacific Plate dives beneath a neighbouring plate; its floor lies nearly 11 km down, deeper below the waves than the world's highest mountain rises above them.
Q 11Which river is generally considered the longest in the world?
The Nile
The Nile runs about 6,650 km north to the Mediterranean; its yearly floods once spread the fertile silt that fed the farms of ancient Egypt.
Q 12Which river carries the most water of any in the world by discharge volume?
The Amazon
The Amazon carries about a fifth of all the river water that reaches the sea, enough to dilute the ocean's saltiness for more than 160 km beyond its mouth.
Q 13Which is the largest lake in Africa by surface area?
Lake Victoria
Lake Victoria was named in 1858 by the explorer John Hanning Speke in honour of his queen; it was already known to Arab traders as Ukerewe.
Q 21An underground layer of water-bearing rock or gravel from which wells draw is called what?
An aquifer
An aquifer can be pumped dry far faster than rain refills it: the Ogallala beneath the US Great Plains irrigates vast farmland, yet would need about 6,000 years to recharge once drained.
Q 22Angel Falls holds what record?
World's tallest uninterrupted waterfall
It is the world's tallest uninterrupted waterfall, with a single plunge of about 807 metres, and is named after Jimmie Angel, an American pilot whose plane bogged down when he landed on top in 1937.
Q 23Until 2019 the kelvin was defined by which fixed point of water?
Triple point
Q 14The Dead Sea's shores are notable for being what?
The lowest land on Earth
The lowest land on Earth, more than 430 metres below sea level, lies there because the Dead Sea fills a block of crust that has dropped down between two faults along a plate boundary.
Q 15The Dead Sea's very high salt content makes swimming there feel like what?
Floating
Floating is effortless in the Dead Sea: so much salt is dissolved in the water that it is far denser than a human body, and bathers simply cannot sink.
Q 16About what percentage of an adult male human body is water?
60%
Water makes up about 60% of an adult male's body weight, a little less in women, and is split between the inside and outside of cells.
Q 17When a chunk of ice breaks off a glacier to become an iceberg, the process is known as what?
Calving
Calving borrows a farming word: since the 1830s a glacier has been said to give birth to an iceberg just as a cow gives birth to a calf.
Q 18A rainbow is caused by refraction, reflection and dispersion of light in what?
Water droplets
Water droplets send the sunlight back the way it came, so a rainbow always appears in the part of the sky directly opposite the Sun, with the Sun at your back.
Q 19In a primary rainbow, which colour appears on the outer edge?
Red
Red sits on the outer edge because each colour is bent through a slightly different angle on its way back to the eye, and red light returns at the widest, about 42 degrees.
Q 20Steam is the common name for what?
Water vapor
Steam is water vapor, the gas phase of water; the white plume seen above a kettle is actually vapor that has already condensed back into a fine mist.
Triple point: only at 0.01 °C and a very low pressure is water solid, liquid and gas all at once, which gave laboratories a mark they could reproduce exactly; the kelvin now rests on a constant of nature.
Q 24The Mpemba effect refers to hot water doing what faster than cold water?
Freezing
The Mpemba effect is the observation that hot water can finish freezing faster than cold water under some conditions; it is named after Erasto Mpemba, who noticed it as a Tanzanian schoolboy in the 1960s.
Q 25Pure water reaches its maximum density at about what temperature?
4 degrees C
At 4 degrees C water is at its densest, so it sinks to the bottom of a lake while colder water stays on top; lakes therefore freeze from the surface down, leaving liquid below for fish.
Q 26What unusual thing does water do as it freezes into ice?
It expands
It expands by about 9% as it turns to ice, with enough force to burst household pipes and, over many winters, to prise open cracks in solid rock.
Q 27Water that leaves limescale in kettles because of its calcium and magnesium content is called what?
Hard water
Hard water carries high levels of dissolved calcium and magnesium; heating leaves them behind as limescale, and they stop soap from lathering easily.
Q 28Water molecules stick to each other by forming what?
Hydrogen bonds
Hydrogen bonds link the slightly positive hydrogen of one water molecule to the slightly negative oxygen of the next; without them water would be a gas at room temperature, as its cousin hydrogen sulfide is.
Q 29The most remote spot in the ocean, farthest from any land, is nicknamed what?
Point Nemo
Point Nemo, the oceanic pole of inaccessibility, lies about 2,688 km from the nearest land and serves as a 'spacecraft cemetery' for de-orbited satellites.
Q 30Dry river valleys and lake beds show that water once flowed across which planet, now a frozen desert?
Mars
Mars keeps nearly all its water as ice today, in its polar caps and under the ground; the air is so thin that liquid water on the surface would quickly boil away or freeze.