I want to desing a creature capable of survive long terms of time without drinking water, but I am not sure how that creature could store water.  
This are my ideas but I am looking for something more efficient or possible:

 - **Increase amount of water in blood:** Each litre of blood has almost half litre of water. Increasing the amount of water in blood could be used to store it but thinking in that I notice a little problem, increase the amount of water in blood would increase the pressure of blood and I don't know if that could be bad. Also I have read in somewhere [quote needed] that if you increase the amount of water in blood, red blood cells start absorbing it automatly (it's a problem of their plasma membrane) until they "explode" and die, huge problem.
 - **Store water inside fat:** Dromedaries store almost 50 kg of fat in their hump, fat *isn't* water but fat *has* water, I don't know exactly the process but when they produce energy with the fat, each kilograme of fat combined with oxygen could produce like waste a litre of water used to survive. It's quite good this idea but I don't want to put a hump in them and also a litre of fat doesn't have exactly a litre of water so it is quite "inefficient".
 - **Special organ:** My last idea is have an inner organ like a bag full of liquid water to store it. Water enter to the organ throught the blood system and when it's needed, it's send to the intestine, where it can be re-absorbed. I find excelent the idea but I don't know any specie who does that so I don't know if that is possible. Also I was thinking to store water in an organic material made of water (or at least hydrogen) and more dense than water, so it can store more water in the same volume, but I don't know any compound like that.

**Edit:**  
I don't like the idea of use humps because:

 - An humps isn't "cute", I don't want to put an hump in their back. Also it's quite heavy and it's a hunter creature.
 - A kilograme of fat produce a litre of water, but a litre of fat **isn't**  a kilograme of fat (I can't find the value), so It's less efficient than store water it self. Maybe you could say that it has the plus of give energy and you are right but my specie is fine with that, it doesn't need more energy backup, I am looking for water backup.