Welcome.
There is not a way to download a specific set of OpenStreetMap tiles compatible with the Map component. However the Map component does cache the tiles in the app that the user has previously visited. Under some circumstances, the component can access the cached tiles when there is no Internet connection. Try using the app without a WIFI connection (after you have previously used it to work with your hydrants, then see what happens when WIFI is disconnected. Does that work for you? See Map and Marker components with OSM map uploaded on sdcard device - #4 by SteveJG
You could also capture a screenshot of your map that displays the hydrants as a png or jpg file. You will not be able to navigate using the jpg but you can have available a map image that will display the hydrant locations.
The LocationSensor works when there is no Internet. The Map might work if the right tiles are cached in the app.