Blood VS Water

I am sure everyone is aware of the old saying, "Blood is thicker than water". And I am sure if you ever went to High School biology class you even proved that it was true, but so is oil and so many other things. And I am sure there are so many things out there that might even be thicker than blood.
I am having a hard time with this concept, I would love to think that it wouldn't matter whether, you have the same blood running through your veins biologically to stick by someone, or to help them out, or to call them sister or brother. I would love to think I am not the only one who thinks like this either.
I hear a lot of times people using phrases like, "she is my ONLY sister". Maybe because I don't have any sisters I don't know what that would be like, but I do have an only brother. I also have a lot of really dear friends and in most cases when talking with people they think I come from a very large family, because of the way I talk about them. I have had numerous people taken back, when I tell them I have only one sibling, and it is because I care so deeply about so many people. My blood is not even thought of in those "friends" as blood or water.
I know some times our deepest hurts come from those we love the most, but I think those are the ones we should be willing to forgive and forget the fastest with. It may just be the water that will wash away the blood in the end anyways! But don't let the water and the blood be the problem or the difference. I have so much family in my life and I don't even know where the blood ends anymore, I think I will leave it that way!