What does "Blood is thicker than water" means exactly?

Question

I know the meaning, that no matter what happens family is still family, or that you support your family over anybody else. My question is about the words. I know "Blood" refers to family, but what does it mean when they say "its thicker than water"?

Answer 1

blood is what gives you life and links you to your family (DNA)

and water is common and its all around you

spill water- so what?

spill blood- OMG!

Answer 2

It means exactly what it says, Blood is thicker than water means "blood"  relatives will be protected in any situations while casual friends and acquaintances who are ""Water" will not.

Answer 3

Family is more important. Always pick your family over your friends.

Answer 4

In societies, they share water.  Mostly in the sense that they "go to the well" for water or they have "bathing pools" or whatnot.  We all share water, but only family shares blood.