How to Create Water & Lava
To create water, you must first select the “Add Terrain” tool from the tools menu. From there, go to the colors menu and scroll down to the bottom of the list. You will find three blue colors that are actually water bricks. Select one of these three water colors and it will be ready to place.
After selecting the color, it is much like placing any other brick with the terrain tool. You can place the water anywhere and however you want.
It is worth noting that there are at least some water physics in the game. Some water can still flow out from the water bricks you place. You can create some very nice waterfall features thanks to this. However, the physics are far from perfect. The water may flow in weird ways. For example, my swimming is pool overflowing with water on one side for no reason.
Once you’re finished placing your water, have fun with it. Maybe go for a nice swim.
A commenter mentioned that painting water will change the properties of the water block, so I’ll make mention of it here. If you try to change the color of a water block with the paint tool, it will turn the painted area into a solid, walkable surface, i.e., not water.
I became curious to see if painting the water would also change the properties of the water under the colored surface. I took my Cole’s Earth Driller and dug under the water (because logic) to take a look. Turns out that it is in fact still all water under there and you can swim in it. The paint tool just creates a thin surface sheet on the water. I think some interesting things could still be done with painting water. Pick the right colors and you can make it look like a layer of ice perhaps?
In case you were wondering where my earth driller is, it exploded. Apparently digging into the liquid water and the solid surface on top of it at the same time was too much. It broke physics, pinged off in the opposite direction high into the skies at astronomical speeds. After about 2 minutes of flight, it crashed into the ground and exploded. R.I.P. Earth Driller.
To add lava to your world, you must first select the “Paint” tool from the tools menu. From there, select the color pattern that is a mix of yellow, orange, and red. This color is your lava.
After selecting the color, you can just paint it on to the landscape however you see fit. You can paint it on to nearly anything. You can even create lava trees if you want.
Unfortunately, you are unable to make lava flow like water does. You can only stick it to surfaces. I am sure that you can still do some pretty cool things with that.
Once you’re done placing your lava, have fun with it. I do not recommend going for a swim in it though.