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Contests over water resources are increasing across the world. This is irrespective of the water availability situation of a region or country. The Food and Agriculture Organization (FAO) of the United Nations (UN) has termed excess water demand over available water supply as a major global development challenge.
Access to water depends upon both water resources availability and the demand for it. On the other hand, demand depends on several factors like the size of the population and its growth, the level of economic growth and water use efficiency.
Many political and socio-cultural factors determine users’ access to water of an acceptable quality. Lack of clean water is also considered as absence of access to water.
Water availability decline is steep in low- and lower-middle-income countries, mostly in Asia, which has the least amount of water but has the highest water withdrawal rate.
Estimates show that if the global water availability decline continues, 87 out of 180 countries will have annual renewable water resources (ARWR) per capita below 1,700 cubic metres per year (m3/year) by 2050.
The number of countries with absolute water scarcity—ARWR per capita below 500 cubic metres/year—is projected to increase from 25 in 2015 to 45 by 2050.
India sustains 17.74 per cent of the world's population with just 4.5 per cent of its freshwater resources. On the face of it, the country seems to be heading towards water shortage. However, the water budget proposed by T N Narsimhan and V K Gaur in 2009 shows that the country still maintains a balance between water demand and supply.
The water budget says that India’s average annual rainfall of 1,170 mm yields 3,838 cubic kilometres (cu km) km of water. Of the total rainfall, 1,869 cu km constitutes average annual potential flow in rivers, while 432 cu km replenish the groundwater.
Evapotranspiration accounts for 40 per cent of the total rainfall. The remaining 60 per cent constitutes the water accessible for human use. Out of this, 1,123 cu km is utilisable water while 623 cu km is currently used. Accordingly, it can be concluded that India’s water demand does not exceed supply.
A re-assessment study carried out in 2019 by the Central Water Commission presents little improved figures for the average annual water resource of the river basins of India for the study period of 30 years (1985-2015).
As per the study, the average annual water resource of the river basins of India has been assessed at 1,999 billion cubic metres (BCM), which is a little higher than the previous estimate.
Out of this, the utilisable water quantity is 1,126 BCM owing to topographic, hydrological and other constraints comprising 690 BCM of surface water and 436 BCM of replenishable ground water.
Looking at the water availability trends, the average annual per capita availability in 1950, 2001 and 2011 was assessed as 3,000-4,000 cubic metres, 1,816 cubic metres and 1,545 cubic metres respectively which may further reduce to 1,486 cubic metres and 1,367 cubic metres in 2021 and 2031 respectively.
This per capita water availability is not same throughout India. It varies spatially and temporally in various regions of India depending upon the rain fall variability, utilisation patterns, evapotranspiration. However, per capita water availability disaggregated data for different uses, geographies and states is not available to comprehend it further.
Major surface water is contributed by around 10,360 rivers and their tributaries (with a length of more than 1.6 km) consisting of 12 major rivers with a catchment area of 253 million hectares (ha) and 46 medium rivers with a catchment area of 24.6 million ha.
The Ganga-Brahmaputra-Meghna system is the largest river system in India with 43 per cent of the catchment area of all major river systems. The total yearly flow in India’s river basins is estimated to be 1,999.20 cu km. However, only roughly 690 cu km of accessible surface water can be used.
This surface water is unevenly distributed over time and space. While some river basins have a vast catchment area and carry enormous quantities of water, others are small and have a comparatively smaller quantity of water.
Most of the Himalayan rivers are large and originate in the snow covered high-altitude areas. As such, they carry sufficient water throughout the year and are called perennial rivers.
In contrast, most of the rivers in South Peninsular India, such as the Cauvery, Narmada and Mahanadi, are fed through groundwater recharge and supplemented by the monsoon rains. They carry no or little water in the dry summer season.
Other than rivers and canals, other inland water resources include reservoirs, tanks and ponds, beels, oxbow lakes, derelict water and brackish water, which cover almost 7 million ha.
They are unevenly distributed over the country with Odisha, Andhra Pradesh, Gujarat, Karnataka and West Bengal possessing more than 50 per cent of these inland water resources.
Monsoon precipitation has been the lifeline of India with respect to agriculture as well as recharging its water resources. India receives about 4,000 BCM of average annual precipitation along with snowfall, of which 3,000 BCM is received in the monsoon season (June-September).
The spatial distribution of precipitation widely varies over the country (2500mm in Assam, according to data from the Central Ground Water Board (CGWB)).
Groundwater is a replenishable resource. Agriculture, industrial and domestic sectors depend heavily on groundwater in India.
As per the Dynamic Ground Water Resources Assessment carried out by CGWB and state governments in 2020, annual utilisable groundwater resources in India are 436 BCM and the annual extractable groundwater resources are 397 BCM.
The annual groundwater extraction for all uses is 245 BCM, out of which 217 BCM (89 per cent) is for irrigation use and 27 BCM (11 per cent) is for domestic uses.
The main source of ground water is recharge from monsoon precipitation. About 58 per cent of country’s annual rechargeable groundwater is contributed by monsoon rainfall.
Other sources of recharge like seepage from canals, tanks, ponds and other water structures and irrigation account for about 32 per cent. Uttar Pradesh has the highest net annual groundwater availability (72 BCM) while Delhi has the least (0.32 BCM).
The extraction of groundwater for various uses in different parts of the country is not uniform. Out of the total 6,965 assessment units (blocks/ taluks/ mandals/ watersheds/ firkas) in the country, 1,114 units in 15 states/union territories have been categorised as “Over-exploited” where the annual groundwater extraction is greater than the annual extractable groundwater resource. These overexploited blocks are also called dark zones.
The overexploited assessment units are mostly concentrated in the northwestern part of the country including parts of Punjab, Haryana, Delhi and western Uttar Pradesh where even though replenishable resources are abundant, there have been indiscriminate withdrawals of groundwater leading to over-exploitation, the western part of the country, particularly in parts of Rajasthan and Gujarat, where due to arid climate, groundwater recharge itself is limited, leading to stress on the resource, and the southern part of India including parts of Karnataka, Andhra Pradesh, Telangana and Tamil Nadu, where due to the inherent characteristics of crystalline aquifers, the groundwater availability is low.
India’s water demand is increasing. Irrigation is by far the largest user of India’s water reserve, with usage of 78 per cent of total reserve, followed by the domestic sector (6 per cent) and the industrial sector (5 per cent). It is a major source of drinking water in urban and rural India and sustains 45 per cent of irrigation and 80 per cent of domestic water demands.
Due to rapid economic growth and demographic changes, water demands in all sectors are increasing. The Union Ministry of Water Resources has estimated that India’s water requirement which is 1,100 BCM per year (in 2017) will grow to 1,447 BCM in 2050.
In another estimate by the National Commission on Integrated Water Resources Development in 1999, water requirement of the country for the irrigation sector alone is going to need additional 200 BCM by 2050 compared to the demands of 2025.
Similarly, other sectors will also have higher water demand. If this trend continues, India is going to face a huge water deficit in the future, especially in the irrigation sector.
It is not just the high water demand that is a challenge. Water pollution is also adding to it. According to the NITI Aayog, a government think tank, about 70 per cent of India’s surface water resources are polluted.
The major contributing factors for water pollution are wastewater from different sources, intensive agriculture, industrial production, infrastructure development, untreated urban runoff and wastewater.
Insufficient municipal wastewater treatment capacity contributes a substantial proportion of water pollution in India. Water quality data from the Central Pollution Control Board shows that organic and bacterial contamination has reached critical levels in waterbodies.
This article was first published in State of India’s Environment 2023 released by Centre for Science and Environment and Down To Earth Magazine on March 23, 2023