This water trivia quiz has 50 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 50 questions with answers and explanations. Play the quiz
Q 01What is the chemical formula for water?
H2O
Each molecule has two hydrogen atoms bonded to one oxygen atom.
Q 02About what fraction of Earth's surface is covered by water?
71%
Seas and oceans hold most of that water.
Q 03Water is often called the 'universal' what?
Solvent
Its polarity lets it dissolve a huge range of substances.
Q 04Unusually, water's solid form is what compared with its liquid form?
Less dense
That is why ice floats; water expands by about 9% when it freezes.
Q 05At standard pressure, water boils at what temperature?
100 degrees C
That is a high boiling point for such a small molecule, thanks to hydrogen bonding.
Q 06The continuous movement through evaporation, condensation and precipitation is called what?
The water cycle
It is also called the hydrologic cycle.
Q 07Which enormous salty surface supplies about 86% of global evaporation?
The ocean
The sun drives the water off its vast surface.
Q 08Roughly what percentage of Earth's water is held in the ocean?
97%
Only a small fraction of Earth's water is fresh.
Q 09Which is the largest of Earth's oceans by area?
The Pacific
The oceans in order of size are Pacific, Atlantic, Indian, Southern and Arctic.
Q 10The deepest known part of the sea lies in which trench, near the Northern Mariana Islands?
The Marianas deep
It is the Mariana Trench, in the Pacific.
Q 11Which river is generally considered the longest in the world?
The Nile
At about 7,088 km it edges out the Amazon, though it carries far less water.
Q 12Which river carries the most water of any in the world by discharge volume?
The Amazon
It discharges more than the next seven largest rivers combined.
Q 13The Blue and White branches are the two major tributaries of which river?
The Nile
They join in Sudan before flowing to the Mediterranean.
Q 14The Dead Sea's shores are notable for being what?
Q 21An underground layer of water-bearing rock or gravel from which wells draw is called what?
An aquifer
A low-permeability layer beside it is an aquitard.
Q 22Angel Falls in Venezuela holds what record?
World's tallest uninterrupted waterfall
It drops 979 metres over the edge of the Auyan-tepui.
Q 23Earth has water in all three states because its conditions sit near what threshold?
Its triple point
At the triple point all three states coexist.
The lowest land on Earth
The surface sits over 400 metres below sea level.
Q 15The Dead Sea's very high salt content makes swimming there feel like what?
Floating
Its dense, briny water is one of the saltiest on Earth.
Q 16About what percentage of an adult male human body is water?
60%
The water is carefully balanced inside and outside the body's cells.
Q 17The phrase 'the tip of the iceberg' reflects the fact that most of an iceberg is where?
Below the water
Only a small fraction shows above the surface.
Q 18A rainbow is caused by refraction, reflection and dispersion of light in what?
Water droplets
In a primary rainbow, red is on the outer edge and violet on the inner.
Q 19In a primary rainbow, which colour appears on the outer edge?
Red
Violet sits on the inner side of the arc.
Q 20Steam is the common name for what?
Water vapor
It forms by evaporation or by boiling.
Q 24Pure water's faint blue colour comes from it absorbing light at which end of the spectrum?
Red
Weak absorption near 750 nm removes red light, leaving a blue tint.
Q 25Pure water reaches its maximum density at about what temperature?
4 degrees C
Below 4 C it expands again, which is why ice forms on top of ponds.
Q 26By roughly what percentage does water expand when it freezes into ordinary ice?
About 9%
The expansion is what bursts pipes.
Q 27Roughly what number of people lack safe drinking water, according to Wikipedia?
As many as two billion
Unsafe water is a major cause of disease and death.
Q 28Water molecules stick to each other by forming what?
Hydrogen bonds
These bonds give water its high surface tension and boiling point.
Q 29The most remote spot in the ocean, farthest from any land, is nicknamed what?
Point Nemo
It lies in the South Pacific and is used as a 'spacecraft cemetery'.
Q 30On Mars, water is found mostly in which form?
Ice
Large quantities of ice sit on and under the surface, though liquid water may exist deep down.