As you are aware, I have strong and scientific grounds for doubting the existence of shallow subsurface fresh water on Mars. Highly concentrated acid brines are a different matter, but you wouldn't want to swin in them, let alone breathe them!

Many of the paradoxes of Mars are actually perceptual ones - they arise, IMHO, because we are trying to force Mars to be an Earth-like planet with abundant free water that has somehow escaped detection. I feel that this is an improper approach and that Mars is in reality as well as appearance a very cold iceworld where free water is an anomaly, rather than the rule. In this scenario, the apparent freshness of the surface is not a paradox, but merely a testament to the glacially slow weathering rate in the thin cold atmosphere.

Hopefully, either MARSIS (Mars Express radar) or SHARAD (MRO radar) will soon put to bed the fiction of shallow accessible liquids and we can begin dealing with the reality of Mars, not the fantasy that we dream it to be.

In this context, novel ideas such as a giant aquarium may be useful ways to address methods of intiating life on the surface of Mars. You will, of course, require a base seal to your aquarium, or it will drain away into the porous soil and fractured bedrock. It may be better to site this on an area of known permafrost since that will be a good impermeable base and will offer H2O molecules to any biota that can survive at those chilling sub-zero temperatures...