scarcity. It follows, then, that one means of addressing potential changes in hydrological circumstances that are uncertain is to ensure that current water management practices are as effective and equitable as possible. This means making all efforts to increase and maintain the productivity of water that is currently available. Such productivity increases need to be sought for both consumptive and in-stream uses. Thus, for example, employment of more rational water pricing practices and the development of flexible schemes of water allocation that will allow droughts and unanticipated shortfalls to be managed in both a timely and effective way could strengthen the capacity of the region to manage its water resources more effectively in the face of climate change and other hydrological uncertainties.


A basic measure of water development and conditions is access to improved drinking water and sanitation systems, as measured by the United Nations on a regular basis. This measure forms the standard by which the water-related Millennium Development Goals were set. Political and social stability is affected by the societal capacity to cope with and adapt to large- and small-scale changes in water availability that may result from glacial retreat and other impacts of climate change on the hydrological system. This societal capacity, often called vulnerability or resilience, depends on conditions that promote human well-being generally. The water-related aspects commonly measured include water availability or scarcity (discussed in the next section) and clean water and sanitation, which are important for human health and general well-being.

Countries in Africa have the most serious problems in terms of the fraction of population without access to these basic water services, but Asia has the largest absolute number of people without access (hundreds of millions), with a wide divergence among countries and within countries. Table 3.6 shows the fraction of the populations in countries of the region with access to “improved drinking” water systems and “improved sanitation” systems, as of 2008 (WHO/UNICEF, 2010). As these data show, urban dwellers are typically more reliably served than rural dwellers, and access to water is typically higher than access to sanitation. However, national-level estimates of improved water and sanitation, even when stratified by urban and rural residence, tend to mask considerable spatial variation in access. Data from the nationally representative Demographic and Health Surveys (DHS),5 for example, suggest that there is greater variation in access to clean water and sanitation in rural districts than urban districts. It is possible, in principle, to use these data to create district-level mappings of access to clean water and sanitation. This could provide finer-grained insight into the geographic distribution of water-related need and vulnerability, including by river basin and proximity to the Himalayas.

TABLE 3.6 Share of Population with Access to Improved Drinking Water and Sanitation, by Country

Improved Drinking Water Improved Sanitation
Urban Rural Total Urban Rural Total
Afghanistan 78 39 48 60 30 37
Bangladesh 85 78 80 56 52 53
Bhutan 99 88 92 87 54 65
China 98 82 89 58 52 55
India 96 S4 SS 54 21 31
Nepal 93 87 88 51 27 31
Pakistan 95 87 90 72 29 45

SOURCE: Data from WHO/UNICEF (2010).


With the preceding analysis in mind, it is not surprising that there are many different ways to measure water scarcity. Water scarcity can occur when problems of water quantity, water quality, or timing mean there is not enough water to meet people’s wants. Scarcity in the physical sense is often defined in terms of arbitrary but useful criteria such as those discussed in the next paragraph. Economic scarcity is customarily defined in terms of the cost of making water available and a willingness to pay. One significant manifestation of economic scarcity is the economic exhaustion of groundwater, which contrasts with physical exhaustion, as explained in Box 3.2. In this section, we focus on simple measures of physical water scarcity, primarily because they are easy to estimate from available data.


5 Data available at

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement