I'll refer to settled water or unsettled water. The first one look calm and undisturbed, while the second look like there are some current and could even angle down to nothing. Cut from the source, unsettled water will dry up as it's merely an extension of the source.

Water will fill-up and settle if there is enough pressure, either from small spaces or nearby water. You can cut your time and ressources usage by using those to your advantage rather then trying to fill directly whatever you want to fill.

Personnally I use thin coridors one block appart as shown below. First a small video on small scale, then the large scale stuff.
http://steamproxy.net/sharedfiles/filedetails/?id=882461036


Small 1x2 pool also work, but are better used on smaller projects.

After I've dug or placed those corridors, I start one block before the last unsettled water to place a new block of water and do that again two square away as shown on these screenshots.


You don't need to worry about waiting for the water to settle, it would only show you what look like your initial target and confirm your in the right spot (costing some time). The picture below was in the exact same spot as the previous one.


This is what it looks like when your ready for the final phase.


Wich is simply removing quickly strip by strip the corridors. Take care there are at least one block of settled water behind you when you start, or if you finish on a corner (better let it settle before you take it or place a block of water in it's place).

Almost forgot this one and it feel like more then a sidenote.

As blocks of liquid below the corridors are not full (notice they don't reach the top of the block?), the technique does not work on additional layer of water above the first one. This seem to be due with liquid pressure applying on too many partly empty blocks as water level does not reach the top of the block.

What's the cure? Personnaly I switch to smaller diagonal patterns, but a little experimentation should give you your techniques for floors aboves.

If you make a hole in water, either by design or by accident, it will never fill up if it's too big (not enough pressure from enough sides).

It may look like this.


To fix it, first surround the hole with solid blocks. Pathway to the rim is optional. Warning : you need to place the rim on the high part because it is really settled water just trying to push forward, if not water will flow over it (then remove that block and place it in the right spot... there will be enough pressure to refill that block's hole).


Then proceed to make a diagonal "chess board" design. Incidentaly, this is how I make second layer for pool of liquids.


Then fill the empty spaces with water.


You can now remove the blocks starting with the "chess board" pattern.



When the middle part is done, you can remove the rim starting with a corner.



And there is a hole no more!

It works on all liquids.

It will cut your ressources usage by roughly 75%! (thin strip technique)

Dont let unsettled water unatended or it will eat up nearby blocks and replace them with more unsettled water (wich in turn will destroy even more, etc).

You can also let the thin strip there, as each block is subjected to water on 6 sides (diagonals counts), they will eventualy disolve. The same goes for the rim while fixing the hole in water. But it has to be a single block in width, or the count of water block drop by half and it won't work.

Simple, you liar you say? Well, simple enough compared to my other stuff ;)