Why do the Combine need water?

[TheOneFreeMan]

Without water in the oceans, the sea floor would be just wet sand and dirt(I believe), and when it would which would be hard to run through.

I would suggest that the ocean is a slightly harder obstacle to run through.

 

[gFrohman]

1. It gives more land for harvesting minerals in the earth's crust.

You can drill for minerals by having equipment in the ocean (such as oil rigs in the middle of the ocean, etc.); this is unnecessary.

2. It makes it hard for the rebels to flee an under-attack continent

It's harder to flee if you're on an island with no boats (more land means more of an ability for rebels to flee on foot).

3. It makes it harder for the rebels to live in general.

This is true; if too much water is taken, the Earth will become unbearably dry (you need enough water on the Earth to keep a decent rain cycle going).

4. More land to make cities for the citizens and metrocops...

As said previously, the human population is dropping, this isn't necessary. More land needed implies a growing birth rate a lot of times; the birth rate during the Combine occupation is zero (which is what you would want for an immortal society to make sure the population doesn't get wildly overpopulated) - the death rate is still around.

 

[DEATH eVADER]

Because they want to rid the world of leeches; the most hated creature in the Universe