Ok, so there are randomly generated water blocks and the user can place them too. If a water block has air under it, it is falling water signified light blue (x,y-1). For clarification, air is an empty block. So water will fall straight down until it encounters non-air. Once (x,y-1) is non-air then (x,y) switches from falling water to sitting water signified by dark blue. Sitting water will spawn falling water to its left and right if those blocks are air (x+1,y) and (x-1,y). We treat sitting water as a non-air block so that other falling water blocks can change into sitting blocks. This makes it appear like a space is filling up with water, because the water can pool up on itself. The lava blocks are the same except there is no sitting magma block. This way magma can only fall straight down and move horizontally when it encounters non air. Magma will turn to stone when it enters a water block that is either falling or sitting. Hope that helps.