Factorio Forums

I use the Jetpack mod. When going "back on earth", it's ok to land on water too - you won't be able to move, but you won't die. If you try to place landfill when standing on water, or even try to place concrete on land, that tile will appear below you, not wasting any items from your inventory. If you mine the concrete you stand on, you die.

When colliding with tiles, placing new tiles will try to fix the collision. That's intentional.