Globally, the planet won't run out, but local populations might. There are many factors influencing availability. Salinity, as you mention, and water that's "l

Globally, the planet won't run out, but local populations might. There are many factors influencing availability. Salinity, as you mention, and water that's "locked up" in other organisms, or in the geology. And don't forget power/political structures that limit access. Then there's cleanliness: ensuring that water is safe is a complex problem requiring infrastructure, energy, transportation, education, governance, etc. Increasing temperature will evaporate more water, forcing us to implement new ways to harvest it. If locations of water harvesting become increasingly disparate, then we are faced with an increasingly thorny logistics problem: transporting the water to where it's needed. With these practical factors, accessible clean water may indeed become limited for an increasing percentage of the population.