The whole point of the alien entity, the TET, in Oblivion is to abstract the earth's oceans because it can use them for power.

But the solar system has a lot of other water according to this article in io9. TET could easily take water from other planets, moons or asteroids and it wouldn't have to do anything nasty to the local populations there (as far as we know). So why does TET want Earth's water?

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    According to director Jospeh Kosinski the TET was actually after Deuterium (heavy hydrogen). - FYI, our two nearest neighbors Mars and Venus both have a higher deuterium-to-hydrogen ratio than water on earth.
    – Oliver_C
    Commented Jan 7, 2014 at 23:32

3 Answers 3


Whilst it's true that other planets contains water deposits, no where but earth contains it in such abundance and so accessible, as the article in io9 states.

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As a rational human being that considers confrontation to be problematic, sure: I'd tap up one of the frozen planets for water underneath. But the TET was perhaps uncaring about the ramifications of ressistance on Earth (which, as the movie reveals, was obviously a fatal mistake).

Also, water only exists in its 'liquid state' on Earth, due to its Goldilocks status. It's probably much easier for the harvesting process to gather the substance in a maleable, liquid form than as huge blocks of Ice that need to be thawed out.

Also, as Oliver C has pointed out, it wasn't the water itself the TET was after, but the Deuterium contained within it. Deuterium is aparrently incredibly easy to extract from SEA WATER using centrifugal force.

A key advantage of deuterium is the fact it can be easily extracted from sea water without harming or polluting the remaining water in any way. It is estimated the world’s oceans contain enough deuterium to supply global needs for many, many generations to come.

So the TET was quite environmentally considerate, it seems! I'd imagine wiping out the worlds population of humans certainly put a stop to global warming. The Nihilists amongst us should be thanking it!

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    And on desolate asteroids you can't tell a good story about human resistance anyway but would have two hours of watching a big white thing melting ice blocks and singing "Daisy Bell" on its own. But an in-universe answer is even better than that.
    – Napoleon Wilson
    Commented Jan 7, 2014 at 22:47
  • Darn human virus! Commented Jan 8, 2014 at 5:18
  • Europa seems pretty accessible. Plenty of water, low gravity well, but then (considers), smack a meteor into the ice and have an orbiting vehicle collect the vapor. It could use a little of the deuterium to offset the drag of passing through the vapor and redirecting the comets. It would not even need to set down. Commented Jan 9, 2014 at 18:50
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    Another thing to consider is that humanity is able to see things fairly easily within our own system. The narrative at the opening stated that Earth was ravaged 60 years earlier, so the harvesters had been gathering for that long (or longer, given the maintenance team were just clones with "memory wipes"). Given enough time, it's possible that we would have noticed them on another planet or moon doing the same thing, so the Tet may have figured it should remove the dominant species from the system, hoard its resources, THEN take them from other objects in our system.
    – MattD
    Commented Mar 20, 2014 at 13:08
  • Having it in liquid form is actually a disadvantage considering that they're transporting it. (What's easier to move around: 10 pounds of water or 10 pounds of ice?) Also, if you need it in liquid form when you're done, gathering it in solid form at the beginning is a very good idea, considering that dealing with heat buildup is one of the biggest challenges faced by spacecraft; you can use your waste heat to melt the water. Commented Jan 4, 2016 at 20:22

Its needing the Earth's seawater is a narrative conceit of story. As the Io9 article states, there are numerous sources of water throughout the solar system which wouldn't require the energy expenditures that attacking a fairly advanced and populated planet, would. Titan, Saturn's moon is almost completely covered by frozen water and there are enough comets in the Oort Cloud at the fringes of the solar system to meet TET's water needs for perhaps its conceivable lifespan.

While this doesn't quite rise to the level of being a "plot hole" it does provoke enough thoughts if one considers it for even a moment to take the scientifically aware viewer out of the suspension of disbelief necessary to thoroughly enjoy the film.

  • Yeah, but less fun than kicking another species' butts! Commented Jan 12, 2017 at 15:05

How can it not be a plot hole, yet create unbelief? You have hit on the fact plot doesn't exist. Only the facts of story as a complete picture.

No, the first answers were correct, and the mystery of what the purpose of the TET ia never described. It could be like the aliens in Independence Day, it could be more aggressive and looking for people rather than simply the deuterium. Maybe it really is trying to fulfill that god role. Maybe it is bent on war against sentient life, dominance, rather than simply if it can get resources. It survived oUT in space, and followed the astronauts home. Malicious intent for unknown purpose, I say.

Oops, was trying to respond to one of those.

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