Adding Magma and Soul Sand
With the Kelp placed in the elevator, head back to the Gravel and get rid of it. This will cause the Kelp to disappear as well. In the Gravel’s place, put a Magma Block and/or Soul Sand. A Magma Block creates a down elevator while Soul Sand creates an up elevator.
Once the Gravel has been replaced with either of those blocks, you should start to see bubbles form in each elevator. This means the process worked and the elevator has been completed. If you enter the elevator, you should be able to go up if you use Soul Sand. By going to the top of the Magma Block elevator and jumping down, you’ll swiftly head down to the bottom of the elevator.
Congratulations, you’ve successfully installed a water elevator in Minecraft, which is one of the most efficient ways to get around.