All right. Let's go over the basics of how water works in Minecraft. I've built a nice flat, plane of stone here to show off some of the mechanics of water, and I've dug a trench that's eight blocks long. I'll select my water in a bucket and right-click on this block to drop it, and you'll see it flow down this trench. This is my source block of water from which all the other water is flowing, and it travels for seven blocks. So, one, two, three, four, five, six, seven, and eight is blank. If I want it to travel more than seven blocks, all I have to do is dig down in elevation here at this seventh block. So, now I have an additional seven blocks that this water is traveling.
If I throw an item in this water stream, I've got an item conveyor. It makes this drop at the seventh block and continues all the way along from point A to point B. Sometimes I've noticed, not always, but items can get stuck here at this drop. This bucket's made it, but every so often, they'll just stay right here. How you mitigate this is to take a second bucket of water, and right-click on this block to turn this into a source block of water. It's still traveling the exact same distance, but now nothing can get stuck in here. So, I'm going to collect that bucket. With your empty bucket selected, you can right-click on this source block to pick that water back up.
You can collect water from the ocean or from streams underground. When you collect water from the ocean, it automatically refills itself. You have an infinite source of water. You can use this to your advantage by making your own personal infinite spring. It's very easy, and it keeps you with plenty of water. All you have to do is dig out a hole that's two by two blocks deep. Now place water in two opposing corners of that block, and you'll see your two source blocks have now become four source blocks. All of this water is still. So if I were to collect some, it refills itself instantly. So I can keep refilling all these buckets infinitely.
Now another thing to remember about water is you can block its flow. You can stop it from flowing by placing blocks in its way. Obviously, if I select this cobblestone, place it here, this water stops flowing, but I can also use blocks that stop the flow of water but leave the space free, like signs. If I place this sign right here, it doesn't have to say anything. The water will stop flowing, but items and I, personally can still pass through this space. So I can use this trick to make a drop where items will fall down as far as I want them to, but the water itself will stay put. Place a sign there and just dig down. Let's dig my way out here and collect this water. Now, if I drop an item into this stream, it'll flow towards the hole and fall down, but the water will stay up top. Other items that block the flow of water but will leave the block free are ladders and pressure plates.
Now arguably, the most important use for water is to protect yourself from lava. If you're out mining, and you happen to accidentally fall into a lava hole like this, you will catch on fire, but you can quickly lay down a stream of water and walk right into it to extinguish yourself. You can also use this water to completely incapacitate this lava. Just turn it into obsidian and cobblestone so you can walk right over it. Simply place the water next to the lava. It flows on top of it and totally extinguishes it. Now, I can just walk safely over this and not have to worry about falling to my death. So, buckets of water, never leave home without them.
Another thing to remember about water is that it will automatically flow towards drops in elevation. So you'll see here, it actually flows towards this canal. It does this if there's a drop up to five blocks away. So, one, two, three, four, five and six. Placing the water here just makes it flow out evenly. So, I'll head over here where I've actually setup four equidistant drops in elevation. If I place this bucket of water right in the middle, it travels out in a nice t-pattern. I can use this to make particular types of item conveyors or just to make a nice design.
I can also place the bucket of water next to the ledge here and create a giant waterfall, which I can use to get safely to the ground. If I fall through it, like so, I fall much more slowly, and when I hit this ground, I'll be completely safe, but one thing to remember is that if your head is submerged, you will start to drown. You can see those bubbles at the bottom there starting to disappear. If they get all the way down, my health will also start to drop.
Now, I can use this waterfall to actually go back up as well. Just get in and hold space bar to start swimming up. I can find a nice position that's half in and half out, so I can still breathe and just wait till I get to the top. This takes a little while, but it is pretty automatic.
So, there you go. Those are the basic mechanics of water in Minecraft.