Rethinking water scarcity: The Role of Storage

Looking at the paper "Rethinking water scarcity: The Role of Storage" by Richard Taylor it covers the topic of water scarcity, its effects on human wellbeing and environment.
In his own lecture he emphasized many times that this term is often used wrong due to the fact that it excludes large water storage areas within the region of scarcity like groundwater, glaciers and soil moisture.
Now I started wondering if this really actually matters that these water sources are not taken into account? After reading many different articles which I reviewed earlier this year almost no one could tell the exact amount of stored water beneath or in case of glaciers above the ground due to lacking data and uncertainties of future climate development. So why would you want to include a source into your "scarcity picture" if you cannot tell it concrete impact on the overall balance? 
Most of the time it was unclear if these water sources were renewable, accessible by poor people with leaking technology or even safe enough to use after they have been contaminated by humans (e.g. in large cities). Soil moisture - even though it is part of the green water circle - does only really add up the overall water balance when it is released into a river or aquifer where it can be subtracted.  Otherwise its only benefit is a moister soil for crop but even that is not sufficient for food growth.
Therefore, isn´t the term "water scarcity" the actual problem rather than its referred sources? 
People suffer from a water shortage when there is not enough for them to meet their day to day minimum needs. So rather than debating if the regions suffering of water scarcity really fall in this category there should be debates on how to supply everyone with sufficient water amounts - no matter if the region suffers of scarcity or not the actual situation for the "poorest of the poorest" should be a measure for leaking water amounts.