however due to the significant variations in water availability across space and time defining terms such as water stress are difficult tasks as a result there are a number of different ways in which the level of water stress can be measured this approach defines water stress in terms of the relationship between water availability and population measuring stress as the amount of renewable freshwater available per person per year according to the water stress index if the amount of renewable water in a country falls below m per person per year that country is said to be experiencing water stress if it falls below m it is said to be experiencing water scarcity and absolute scarcity if below m falkenmark et al however it also has limitations in that it ignores variability in water availability within countries fails to account for the accessibility of water does not consider anthropogenic sources of freshwater such as desalination plants and dams which increase water availability beyond natural flows in a given year and does not account for the fact that different countries and regions within countries have different demands for water rijsberman