Well if it's solar powered, we can easily take it out with an inexpensive sticky black paint bomb. Second, while you won't run out of water, you will run out of

Well if it's solar powered, we can easily take it out with an inexpensive sticky black paint bomb. Second, while you won't run out of water, you will run out of other stuff for your hydrogen IED drones. Now a much better thing to do instead of making IED drones would be to melt sand or rock into appropriately formed projectiles so that one has an autonomous artillery piece that does not require reloading. There are much better explosives to use than hydrogen. One could use the haber process to make ammonia and use some biological carbon sources to make pretty much any explosive worth using. Landmines are probably cheaper though.