Building block container is a modular hollow building block that may be used to build a wall, shelter, structure, building, greenhouse, water filtration device, emergency shelter, pipeline, flood blockade, floodwall, dock, or raft. Building block container has a special design so that they are reversibly attachable to each other without fasteners. Building block container may also be used as a container to hold any type of liquid or solid contents. A plurality of building block container may be shipped to a disaster area, third world location, or anywhere with people in need, while filled with water or food, where the water or food may be consumed by those in need and then the empty building blocks may be used to build a wall, shelter, structure, building, etc. One or more building block containers may also be used as a water filtration device to filter unclean water into drinkable water.