Liquids are a type of block in Mine Blocks that have an interesting physics.
A liquid source block is the block in which more liquid can flow out of (to a certain degree). Only the source block can be collected with a bucket. Once a source block is collected, the non-source blocks will eventually trickle out to nothing.
Source blocks play an important role between lava and water. When a lava source block comes in contact with any kind of water, it will turn into obsidian; however, if a non-source block of lava comes in contact with water, it will turn into cobblestone.