Finite Liquid is a mod that's been around for some time now. It's made by djoslin, who rewrote it several times, and still keeps updating it with new stuff today. He recently rewrote it once again, for 1.8, so I checked it out to see what it's all about.
The first thing you'll notice when you launch Finite Liquid is that world generation is taking a while. This is because the mod needs to convert the regular Minecraft water into the Finite Liquid water. The physics are changed drastically. While regular water in Minecraft, doesn't move, is infinite, and spreads only to some degree, with this mod water will become more dynamic and, as the mod states “finite”. If you find a small 5-6 block pond, and break more blocks, the water will spread to the spaces where the blocks used to be, but the level of the water will drop too.A lake I drained by digging a hole to a cave system beneath.
The ocean and all water bodies adjacent to it, however, will not drop in level since it is so big. If you find an entrance to a cave near the waterfront, digging a trench between them will cause the water from the ocean to start slowly filling the cave, and everything in it, until it's so filled it reaches the same water level as the ocean.
A ravine being flooded.
Now, this all probably sounds extremely confusing when put into words, so why not let this video, made by the mod's creator, clear it up:
Flooding a ravine with ocean water, or draining a lake into a cave is incredibly fun, so this mod isn't all about mechanics, but fun too.
Now, with all these water changes, the modder had to implement some machinery to manipulate it. There are pipes, pumps, grates and liquid detectors. These do exactly what you think they would, and can be used to create simple contraptions, like waterfalls that loop, but also more complicated stuff for the redstone enthusiasts out there. Rain has been changed to generate small puddles of water on the ground, which disappear after a while and are completely useless, but really help the atmosphere.
Puddles that are created when it rains.
But wait, there's more! This mod also changes the way lava acts into something between regular Minecraft lava, and Finite Liquid water. It also adds oil, which is a flammable liquid and can be found underground, and methane, which is a gas that can also be found underground, and is also flammable (and can explode in certain situations). It's worth noting that “flammable” means torches also set it on fire, not just flint and steel and lava. This can cause some unwanted explosions while mining, so you have to watch out when placing torches. Methane can be spotted as it is displayed as a slight blurred purple tint instead of the regular air blocks.
The mod also adds sponges at the bottom of oceans, which can be used to soak up water and squeeze (right click) it back out of the sponge block.
Bugs are present, but not too common or big. I experienced little to no slowdowns, even when I was flooding ravines, which is truly remarkable considering the amount of calculations being done. Some users are reporting ocean water to be glitchy or even not work at all, but in my hours with the mod, I didn't experience this issue.
All in all, the Finite Liquid mod provides a lot of realism to Minecraft, some cool new mechanics and features, and helps the atmosphere. It has it's fun parts, too, so it really is a full package of a mod that will enhance your Minecraft experience if you install it. It does however edit a lot of core Minecraft classes, which, as all you pro modders out there will know, can cause unwanted conflicts with other mods. If you don't have a stock-full minecraft.jar, I'd recommend you give this mod a try.
Check it out here on the mod's thread, or on the official site.