When building a base tile on a block that already contains water the water isn't moved above the tile, (as is the case with objects like seeds) Water simply vanishes completely, so while trying to reinforce the underside of a source of water you end up destroying entire full blocks of water in the process.
upon further testing the process can also be replicated in an enclosed airtight space to show that tiles also delete any air on their location when built, the tiles are successfully moving solid objects out of the way but annihilating Liquids and Gases.
To Test liquids: Find a source of water and build any number of tiles within it. the water level will remain constant after the tile is built. Deconstruct the tile and the water level will lower. Repeat with enough tiles to cover the entire water supply and the entire water source with be gone without any evidence to why. To Test Gases: Start a new colony and block of any oxylite with tiles to create a completely sealed room. Place as many tiles as possible within the room. the pressure of the gas on any open tiles will not increase. Deconstruct all placed tiles and then rebuild them. the value of oxygen and carbon dioxide in the air will deplete rapidly as this process is repeated until your duplicants suffocate.