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 1 700 m3 per person per year, that country is said to be experiencing water stress, if it falls below 1000 m3 it is said to be experiencing water scarcity, and absolute scarcity if below 500 m3 (Falkenmark et al., However, it also has limitations in that it: 1) ignores variability in water availability within countries, 2) fails to account for the accessibility of water, 3) 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 4) does not account for the fact that different countries, and regions within countries, have different demands for water (Rijsberman, 2006).