It is suitable for water meters that require a dedicated key to unlock. The keyhole usually looks like this:

It was initially modeled based on the precise tools shown in this video. The instructions for use are also in the video.

You don't actually need to turn it like turning a key. There should be a lever that you pull in the direction facing the street, or in the opposite direction to the key slot. Insert the key and press the lever by tilting it.
These can be printed in batches of five. If you hand out a few during a winter storm, they'll be a great free gift for your neighbors.