Water Challenges / Better Kidneys?

Many parts of the world are experiencing fresh water shortages, due to population pressures and global warming that is shifting the distribution of rain and snow water. Desalination plants are one solution but are costly to build and operate. Seawater is abundant, but is unfit for human consumption, largely because the human kidney cannot concentrate salt efficiently.

"Other land animals and marine animals such as fish, whales, and penguins can adapt to saline habitat. For example, the desert rat can survive by drinking seawater because its kidney can concentrate sodium far more efficiently than the human kidney." -- Wikipedia

A genetic engineering opportunity exists to endow humans with genes from mammals, such as dolphins, whales, or desert rats, that CAN drink seawater without ill effects.

It might be objected that this is inhumane, to engineer humans to endure "sub-human" conditions. However, if fresh water shortages persist indefinitely, children receiving the ability to drink saline water might consider it a gift. It should be cheaper and far less energy consumptive than building extensive additional desalination capacity.

A late mutation enabled humans to digest milk beyond their suckling period, conferring a big survival advantage. Most of us are descended from ancestors having this mutation. Every time you consume milk or milk products you leverage it. So, would the novel humans who could drink seawater possibly out-compete and displace prior (old style) humans who could not? And would they be complaining about having been given this valuable super-human ability?

Paraphrasing Wikipedia, the human system regulates blood salinity in a tight range, but the human kidney is inefficient at concentrating salt, so to remove excess salt it must excrete large amounts of water, causing dehydration. Ocean salinity varies around the globe*, but remains relatively constant across geologic time, due to processes that remove salt.

A novel human kidney that can concentrate salt into a brine would help humans better survive and compete in a freshwater-challenged world. They could drink saline water as easily as you and I can drink milk. And the fix is a permanent one, since sea salinity remains roughly constant over eons of time.

* The salinity of seawater ranges from 3.1% to 3.8%, with 3.5% regarded as typical.

Reference: http://en.wikipedia.org/wiki/Seawater