What fresh water is not readily available for use?

Answer 1

This can be a complicated question, and I doubt I can do an adequet job answering it, but here goes . . .

Some freshwater is locked in ice.

Other sources are contaminated - either with dangerous microbes or potentially poisonous minerals. Lakes near mines, for example, may have trace to high levels of waste chemicals from the mine - either left behind because it was found in the mine and unwanted, later to seep into the lake, or perhaps due to chemicals used to help process or purify the ores before shipping, so that less of what is shipped is unwanted impurities.

These can be cleaned, but often the cost is higher than the cost of selling the water afterwards. No company will operate if bankruptcy is inevitable.

Also, some water can be difficult to reach. It may be located at levels too deep to drill - or beneath stone to costly to drill through for the amount predicted to be gained from the drilling. Or it may require long canals to redirect it towards the site of need. The cost of the canal may be cost prohibitive - or the canal cannot be dug for environmental reasons (perhaps it would cut across a nature reserve or through a meadow where an endangered bird lives).

Answer 2

Most of the Earth's fresh water is unavailable because it is in untapped aquifers underground, or frozen in ice caps and permafrost. Theoretically, fresh water could be harvested from sea ice, but most is obtained from rain, snowmelt on the surface, plants, and water vapor in the air.