Should I hold in a wee to stave off dehydration?

The following question was asked by my dad:

If I was stuck in an arid place, like Mars for instance (or a desert) with no access to water supplies, should I resist the urge to wee so that I conserve the liquid content in my body for as long as possible in the hope that I will find water before I completely dehydrated?

Before I answer please consider that I am not medically trained, so don't take my word as gospel: I'm just researching this with the resources available to me, and it's a little outside of my normal interest-base. I'd appreciate clarification and correction on this issue by anyone who knows better than me!

There are two things that strike me with this one:

1. As far as I understand it, once your body's waste water collects in your bladder, then that's it. It's there until you pass it out of your body and is just dead weight that you're carrying around; it is put to no further use inside your body, and I don't think that there is a mechanism by which the body draws water back out of the bladder in times of dehydration*.
2. Again, as far as my understanding goes, the main (if not sole?) purpose of urinating is to get rid of dissolved waste products and substances from the human body. Even if it were possible to reintroduce the contents of your bladder to your blood stream via some internal method, would this potentially be more dangerous than being dehydrated?

So I'd say no, don't hold it in if you're dehydrated. At best, it appears that it would have no effect on your level of hydration whatsoever. At worst, there seems to be potential for it to actually make things worse.

Other questions that enter my mind on this subject include:

• Would the act of urinating in such a situation have any measurable contributing to lowering your body temperature?
• Is it safe to drink your own urine, and would this be a viable option for prolonging your life in a dehydration situation**?
• Would it be worth the time and effort filtering or otherwise attempting to purify your own urine before drinking it?

Before I go I'll say once more: in all honesty, I don't know what I'm talking about. These are just comments on what feels logical to me after a bit of research here and there. If you know better, please feel absolutely free to comment below and correct me.

* To people with cleverness in relevant fields: I'm assuming that the bladder collects water by an osmosis-type process, so if the relative water content of the water in your bladder and wherever it usually comes from to get there is reversed, would the direction of osmosis be reversed? And if so, would it be the case that you'd already be thoroughly dead by the time it got to this point?

** opinion seems to be divided on this matter- the most convincing sources I've found suggest that it's fine to drink your own urine for a couple of days as healthy wee is 95% water, but each time you urinate the concentration of waste products gets higher, resulting in eventual dehydration and/or renal failure