Water is a very important resource in Minecraft- without it, it is impossible to get ahold of any food over an extended period other than apples- without the use of water for farming, you will run out of animals to kill for meat. Without water for farming, you can’t get wheat to make bread or melon to eat. Without water, you cannot fish. Without water... your game is going to be very short.
That said, it’s time to discuss it- water, that is.
Water basically comes in two forms- source blocks and water flow. Water source blocks are an essentially infinite source of water. Placing a water source block without something to contain it will result in water spreading out from the sides of it- and downwards as well if possible. Waterfalls will go as far as they have to in order to reach a splashdown point, with no limit. Across level ground, though, water will only spread for about seven blocks, lowering in level the whole way. Water source blocks are also the only form of water that can be collected in a bucket. Using a bucket on a flow of water won’t get you anything- just a tiny waste of time.
Water source block sare invaluable, though- fortunately, they are plentiful. Whenever you see a lake or piece of ocean that was formed by the game on creation, you are looking at a mass composed entirely of water source blocks. Water sources can also be found underground in caves, mines, and occasionally just sitting there in the middle of the stone and dirt waiting to be discovered.
It is possible to swim in water. Using the jump button, you will rise in brief bursts- or continuously if you hold the button. This is a good thing, because you can drown if you stay underwater for too long. It is even possible to swim up waterfalls, although the going tends to be slow. Because of this, if you can set up a waterfall in your home that you can turn on and off, you can make yourself a thoroughly secure route into and out of your house- if the waterfall is off, anyone who cares to intrude will have a lot of building to do in order to reach you.
Water can also be used to gather dropped items- any objects dropped into flowing water will follow the water flow to its end.
Furthermore, water can protect places from explosions- especially Creeper explosions. Creeper explosions will not destroy blocks on the far side of water- although nearby animals, monsters and players will be injured just as though the Creeper had exploded on land.
It is also possible to build a boat, which will let you travel by water without having to swim- and without risk of drowning. If your World includes a large ocean, this may be a good way to cross it in search of interesting land or a new place to build in.
However you slice it, water is important in Minecraft, so it’s a good idea to keep track of how to use it and what it can do.