About 70% of the earth's surface is covered in water. While the total supply of water is fixed, it does cycle from ocean to atmosphere to land, and back to the ocean through the water cycle. However, this does not change the total available water, which is finite.
Unfortunately, humans can't use seawater for household or drinking purposes unless it has been treated, which can be very expensive.
Some water can be used without needing any sort of treatment, but the majority requires treatment before it is usable. Once water is found at its source, it is transported to a water treatment facility, like the one shown below, that can remove harmful contaminants and materials.
After that, it is taken to a storage facility, like the water tower shown below, until it is needed. Once needed, it will be distributed for use by things like faucets and sprinklers.
Presently, water has a number of uses, such as for drinking, in the household for food preparation, toilets, bathing, and cleaning, as well as by fire departments for fire protection or by industry for various uses.
Water is not used equally across the planet. Different regions use water differently per capita. Developed regions like the United States and Europe use the majority of water, though developing nations hold the majority of the world's population. This chart shows average water use per person per day in various nations.
At the making of this tutorial, India and China hold approximately 35% of the world's population, yet only use around 80 or 140 liters per person per day respectively, while the United States averages almost 600 liters per person per day and holds only 4.4% of the world's population.