I can think of at least 2 movies that had aliens invading Earth for water.
Is this a feasible motivation? I was thinking that
- Water is H20, i.e. dihydrogen monoxide
- The vast majority of the universe is made of hydrogen
- Oxygen is also pretty common as it's the 3rd most common element in the unverise
- We can combine the raw elements into water, so certainly an alien species so advanced as to be capable of interstellar travel to Earth could also easily combine these 2 abundantly available elements into water
But OTOH I'm not an expert and large teams of people working on big budget Hollywood films seem to think it's a reasonable motivation.