Wednesday, 16 November 2016

Failure of Water Stress Index as a sanitation indicator


In the previous post I outlined the basis of the Water Stress Index and how it can provide an idea of sanitation levels around the world. However, as I said, there are many components that the Index fails to take into account: spatial and temporal variations, quality and access to water, all of which hugely affect sanitation.

Lack of access to water is not necessarily a consequence of a national shortage; in fact, very often significant numbers face inadequate access to clean water despite living in a country that is not water stressed. This is because of economic and physical barriers affecting availability, which vary from place to place. Affordability and infrastructure play a major role, and differences are especially marked between urban and rural areas. For instance, in sub-Saharan Africa only 5% of the rural population has a piped water supply in their homes, in contrast to 35% of urban residents (UNEP 2012). The most important factor that affects urban water usage in East Africa is whether households have access to a functioning piped system. During the 1960s, a person in a piped household consumed eight times as many litres as someone in an unpiped household. In 1997, the latter walked on average about 300m to unprotected sources to obtain water, increasing the risks of poor hygiene and water-borne diseases (Thompson et al. 2000). This demonstrates that although an area may physically have sufficient water (especially when considering water storage and groundwater, not accounted for in the Index calculation), it is not inexpensively, easily and safely available to all. It is access to and quality of water that define sanitation.

Water quantity in a country changes over the course of the year; seasonal differences are not taken into account by the Water Stress Index. As an annual national average, the Index does not take into account that at some times of year there are great quantities of water present, whilst at others there are severe shortages. Rainfall and river flow (especially the upper course) can have strong seasonality in sub-Saharan Africa and is more and more variable between years as a consequence of global climate change. In Namibia, though renewable water resources are plenty (at 45.5km3 per year, or an average of 26,300m3 per year), river flow is extremely seasonal (Taylor 2004). In the month of February rainfall is around 66mm, but in July it is roughly 0.6mm (World Bank – see graph). The changes in water availability force individuals to ‘draw water from a mix of sources through the year’. This is not investigated at all by the Water stress index, suggesting that it cannot represent the ‘spatial and temporal variability in the supply and demand of water’ (Taylor 2004: 14).


Average monthly rainfall for Namibia 1960-1990. Source: World Bank 


A question that must be addressed is: what do we actually mean by ‘water scarcity’? According to Frank Rijsberman (2006: 6), it is when many people in an area are ‘water insecure’ (do not have access to safe, affordable water to meet drinking, washing and livelihood needs) for a ‘significant period of time’. In truth, there is actually no widely accepted definition, since it must be considered very much on a case-by-case basis. What can be deemed “scarcity” depends on how needs are defined, the potential proportion of the resource that could be made available, and temporal and spatial scales. A vital element of good sanitation is full and constant access and use of safe water sources. Nevertheless, in some of the most water scarce countries in North Africa, sanitation levels are high. This is because of other factors also affect sanitation, such as the prevention of food contamination and access to sewage infrastructure or flush toilets. In 2004, Morocco had a coverage of improved drinking water resources of 56% in rural areas, but the improved sanitation rate in these same areas was almost 75% (UNICEF 2006). It is extremely questionable whether there is truly a relationship between water stress and low levels of sanitation.

A measure as one-dimensional as Falkenmark’s Water Stress Index does not capture the essence of water scarcity, let alone what this means for sanitation. To use the Index as a main indicator for sanitation would be to say that sanitation is principally affected by water quantity in a country, without looking at other factors that determine sanitation: affordability, quality, infrastructure for water provision, investments in sanitation facilities, health literacy… The Water Stress Index does not illustrate access to clean water, nor how this varies over time and space, and therefore fails to indicate how sanitation and water truly correlate.


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