Market instruments and institutions for reducing pollution in the Ganga River Basin

The Ganga Basin is spread over an area of 1,086,000 km² in India, Tibet (China), Nepal, and Bangladesh. It drains an area of 861,452 km² in India from 10 states and 1 Union Territory. The basin has a maximum length and width of approximately 1,543 and 1,024 km, respectively.

The Ganga rises in the Gangotri glacier in the Himalayas at an altitude of about 7,010 m in Uttarakhand state of India. The total length of the river up to its outfall into the Bay of Bengal is 2,525 km. The principal tributaries joining the river from the west are the Yamuna and the Son. The tributaries joining from the east are Ramganga, Ghaghra, Gandak, Kosi, and Mahananda. Chambal and Betwa are the two other important sub-tributaries. Nearly 66% of the total basin area in India is agricultural land, 4% is covered by water bodies, and there are large areas under forests and wastelands (National Water Informatics Centre, n.d.).

The rising pollution of the river has been receiving attention from ecologists, environmentalists, and water resources managers since the 1990s. There are several hundred cities and towns located on the banks of the Trunk River, its tributaries, and sub-tributaries. Several millions of people depend directly on the river water for drinking and domestic uses. Hundreds of urban utilities tap the river water or water below the riverbed for municipal water supply. Several thousands of industrial units tap the river water for manufacturing. The partially treated and untreated industrial effluents and municipal sewage being discharged into the trunk river, its tributaries, and the other water bodies and on land have been polluting them. The river system, which is fed by rain and snowmelt, replenishes the largest and deepest aquifer system in Asia. The river network is perennial in most stretches, making it usable for navigation. Hundreds of large and medium-sized reservoirs and barrages built on the river provide the largest extent of irrigation among all the river basins of India.

In 1984, an action plan, popularly known as the ‘Ganga Action Plan’ (GAP) was prepared by the Department of Environment for the immediate reduction of pollution load on the river on the basis of a survey carried out by the Central Pollution Control Board in the same year. The GAP Phase I was started in 1985 to improve the quality of water in the river to acceptable levels by preventing the pollution load from reaching the river from both point and non-point sources (Department of Water Resources, River Development & Ganga Rejuvenation, n.d.).

Since GAP-I did not cover the pollution of the entire Ganga, GAP Phase II (GAP-II) was launched in stages between 1993 and 1996. Various shortcomings in the monitoring mechanism and execution of schemes under the GAP were pointed out by an audit report in 2004. The audit report of the program for the period 1993–2000, for a total fund release of Rs. 655.23 crore, stated that the GAP had met only 39% of its primary target with respect to sewage treatment. There were heavy shortfalls in the achievement of targets vis-à-vis the creation of assets and facilities under the plan (Public Accounts Committee, 2004). After 2 years of implementing GAP-I, in 1987, a judgment¹ was passed by the Supreme Court of India on a case filed by M. C. Mehta for the closure of tanneries in Kanpur that failed to take the minimum measures required for the treatment of industrial effluent, invoking the provisions of Articles 48A and 51A of the Constitution of India; the Water (Prevention and Control of Pollution) Act, 1974; and the Environment (Protection) Act, 1986 (Supreme Court, 1987). According to the Supreme Court and National Green tribunal orders mentioned in the National Mission for Clean Ganga, the latest follow-up regarding the case was carried out in 2017 (C.WRIT PETITION No. 3727/1985 and M.A. No. 594/2017 and 598/2017).

In sum, the past works on pollution in the Ganga River Basin have failed to take a comprehensive look at the various factors contributing to pollution of the basin's water resources and what needs to be done to prevent and control pollution. The focus has always been on point pollution from industries and urban areas.

The work on water quality management lacked a regional outlook in the sense that the spatial patterns of water quality deterioration were never analyzed. The focus was on some cities, which are sources of concentrated pollution load. The relationship between various water quality indicators that exist in the basin is the least understood. Furthermore, very little attention has been paid to non-point sources of pollution. Also, there is too much emphasis on surface water quality and the least attention is being paid to groundwater despite the latter being the largest source of irrigation and domestic water supplies and the huge risks associated with its contamination. The main source of non-point pollution of surface and groundwater bodies in the Ganga basin is agricultural runoff. Fertilizers, pesticides, and salts contained in irrigation water are considered as the main pollutants. The groundwater in irrigated areas gets polluted as these fertilizers and agrochemicals are drained out of the root zone to recharge the shallow aquifer (Chowdary et al., 2005). The nitrates from fertilizers, dissolved in the percolating water from the rice fields, are a major source of pollution of groundwater². Nitrogen and phosphorus are the main drivers of eutrophication in rivers and streams.

More importantly, groundwater and surface water interact in the basin, with surface water contributing to groundwater recharge in certain localities and groundwater discharge contributing to the lean season flows in certain regions. Finally, the solutions prescribed for controlling the pollution of the Ganga River have been mostly techno-centric, involving over-engagement with treatment technologies, while very little attention has been paid to behavioral change aspects in terms of water use and economic viability issues, both of which are crucial for sustainable water quality management.

This article takes an integrated approach to water quality management of the Ganga River, considering the hydrological and ecological integrity of the basin, thereby giving due consideration to the hydro-climate, the quantum and pattern of surface water flow in different river stretches, the vulnerability of groundwater to dispersed pollution, and the dynamics of surface water–groundwater interactions.

The article systematically analyses the water pollution challenges facing the Ganga River Basin from a systems perspective and the ways to tackle them from physical, technical, and institutional perspectives. The study used an eclectic methodology. Knowledge about the basin's river systems, hydrology, and aquifer system was generated using a synthesis of published reports of the official agencies and scientific papers published in peer-reviewed journals. The spatial and temporal changes in groundwater condition in the basin were analyzed using the data of pre-monsoon depth to water levels, for the years 1996 and 2019 for a total of 1,384 monitoring stations spread across the basin. The spatial and temporal trends in the quality of surface water in the Ganga River and its tributaries were assessed using data on eight parameters, viz., temperature, pH, dissolved oxygen, biochemical oxygen demand (BOD), conductivity, nitrate, fecal coliform, and total coliform, for a total of 100 monitoring stations (with annual average values) across the basin for the years 2012 and 2020.

The analyses of factors causing pollution and the issues with the current approach to pollution control and management and their resultant impacts on the water resources of the Ganga River Basin were made on the basis of a review of several scientific articles, especially those dealing with non-point pollution of groundwater and surface water and economic viability of wastewater treatment, and expert knowledge. Knowledge and insights from disciplines such as environmental economics, ecological economics, and behavior sciences available from the reading of select works, and the expert knowledge of the physical and socio-economic realities of the Ganga River Basin were extensively used to distill ideas vis-à-vis what can be done to mitigate pollution in the Ganga River Basin.

As regards water systems, there are reportedly 825 reservoirs in the Ganga basin. The Ganga basin consists of about 276,947 surface water bodies. The water bodies having a size in the range of 0–25 ha account for 98.9% of the water bodies in the basin. There are 23 major water bodies with a size greater than 2,500 ha. The number of water bodies in the Ganga basin by size is presented in Table 1.

There are many water resource projects in the basin, which include major and medium irrigation projects, extension, renovation, and modernization (ERM) projects, and hydro-electric projects (see Table 2).

The aquifer system of the Ganga River Basin is one of the most complex yet most extensive aquifer systems in the world. The majority of the basin area is underlain by a multilayered alluvial aquifer system with high effective porosity and permeability. The aquifer systems extend from the southern part of Haryana and western Uttar Pradesh to West Bengal. The basin also has hard rock formations with limited groundwater potential in the southern parts, falling mostly in Madhya Pradesh, Jharkhand, and the Bundelkhand region of Uttar Pradesh. The parts of the basin that fall in southeastern Rajasthan have crystalline rock formations. The parts of the basin falling in the Uttarakhand region have crystalline formations with very poor storage potential (source: based on CGWB, 2012: Plate VII, p. 16).

The groundwater regime of the basin is influenced by the geology, climate, physiography, land use pattern, and hydrologic characteristics. The natural conditions affecting the groundwater conditions are climatic parameters, such as rainfall, river flows, local storages (ponds, tanks, lakes, and reservoirs), return flows from irrigated fields, canal seepage, and evapotranspiration, whereas anthropogenic influences include aquifer pumping, recharge due to irrigation systems (canal seepage and irrigation return flows) and other practices such as wastewater disposal.

The moderate to high and very high rainfall in the alluvial formations with sandy and sandy loam soils results in good infiltration and recharge, especially in the areas with a sub-humid climate. The total annual replenishment of groundwater in the Ganga basin is estimated to be 171.57 Billion Cubic Metres (BCM), of which 35.1 BCM is reported to be through replenishment from canal irrigation due to canal seepage and return flows from the irrigated fields (GOI, 1999: Table 3.9, pp. 42). In addition to the dynamic groundwater resources, the basin also has a large stock of groundwater, estimated to be 7,769.1 BCM (GOI, 1999: Table 3.11, p. 46).

Groundwater drawdown is comparatively higher in the Upper and Middle Yamuna sub-basins, the Banas sub-basin, and the lower Bhagirathi sub-basin regions. In the Lower Chambal, Damodar, and Upper Bhagirathi sub-basin regions, a rise in groundwater levels is observed. A high drawdown in groundwater levels is observed in the Sundarbans delta. This could be because of the higher demand for water in the fertile delta and an increase in the abstraction of groundwater to meet the needs of the large population in that region (Figures 2–4).

The land use and land cover data for Ganga basin for 2005–2006 and 2017–2018, derived from land-sat imageries, have been analyzed to understand the land use change. It showed that the area under agriculture has marginally increased from 564,866 km² in 2005–2006 to 568,497.85 km² in 2017–2018. In addition, the forest area increased by 12,000 km² in 2017–2018. The increase in area under forests may be attributed to plantations in some parts of the common lands since a notable reduction in area under wasteland and grasslands is also noticed. The area covered by snow/glaciers rose by about 1,030 km² in 2017–2018. The average current storage, sub-basin-wise, is presented in Table 3. On average, about 5.66 BCM of water storage was observed in the Sone sub-basin from the two reservoirs India Water Resources Information System (INDIA WRIS). Nearly 0.06 BCM of water storage was observed upstream of the Gomti Confluence to Muzaffarnagar. The total storage for all 17 reservoirs together is about 15.9 BCM.

Water pollution caused by chemicals from mining and other industries is a major threat to the river. The National Water Quality Monitoring Programme does not provide data on the parameters that are needed to study industrial pollution, directly. Apart from the basic parameters studied, toxic metals such as As, Cd, Hg, Zn, Cr, Pb, Ni, and Fe; pesticides are analyzed once a year, based on needs (CPCB, 2008). However, a thorough spatial and temporal analysis of these pollutants is not conducted due to the non-availability of data.

A better assessment of the temporal change in the quality of water in the Ganga River and its tributaries vis-à-vis these parameters between the years 2012 and 2020 can be made by categorizing the changes in the area corresponding to different value ranges of these parameters, as shown in Table 4. Here, the negative and positive values represent a decrease and an increase in the area, respectively. Table 4 shows that the area corresponding to the high range in temperature (20–30 °C) of surface water dropped during the period from 2012 to 2020. However, the area corresponding to a high pH value (7.4–8.0 and 8.0–9.0) increased during the same period, indicating a further increase in alkalinity. The area corresponding to high BOD (7.0 and above) dropped substantially. The area corresponding to high values of electrical conductivity (above 149 μmho/cm) and nitrates (above 2.4 mg/L) in surface water reduced drastically. The area corresponding to a high fecal coliform count (above 1.22 × 10⁶) dropped significantly. Similarly, the area corresponding to a high total coliform count (above 4.4 × 10⁶) also shrank substantially. In summary, this means that nitrate pollution has increased, as indicated in higher EC values, whereas microbial pollution has decreased – this suggests that point source pollution from urban wastewater treatment plants has reduced, whereas non-point pollution from agriculture has increased.

The Ganga River is severely polluted as a result of the waste generated by the 400 million people who live close to the river. Sewage from many cities along the river's course, industrial waste, and religious offerings wrapped in non-degradable plastics add large amounts of pollutants to the river. The problem is exacerbated by the fact that many poor people rely on the river on a daily basis for bathing, washing, and cooking. The main causes of pollution in the Ganga River are the increase in population density, various human activities such as bathing, washing clothes, bathing of animals, and the dumping of various harmful industrial wastes into the rivers (Pratapwar, 2019).

On the banks of the Ganga, a large number of cities, such as Kanpur, Prayagaraj, Varanasi, and Patna, are hosting industrial facilities such as tanneries, chemical plants, textile mills, distilleries, slaughterhouses, and hospitals. These contribute to the pollution of the Ganga by dumping untreated waste into it (Pratapwar, 2019). One coal-based power plant on the banks of the Pandu River, a Ganga tributary near the city of Kanpur, burns 0.6 million tons of coal each year and produces 0.21 million tons of fly ash. The ash is dumped into ponds, from which a slurry is filtered, mixed with domestic wastewater, and then released into the Pandu River. Fly ash contains toxic heavy metals such as lead and copper (Pratapwar, 2019).

It was observed that the copper concentration from the wastewater released in the Pandu River is a thousand times higher than in uncontaminated water. Industrial effluents contribute to about 12% of the total volume of effluent reaching the Ganga. Although they have a relatively low proportion, they are a major cause for concern because they are often toxic and non-biodegradable (Pratapwar, 2019).

The Ganga basin is one of the world's most important and heavily exploited aquifers for groundwater. Agriculture alone consumes more than 80% of the Ganga basin's groundwater (Upadhyay, 2022). Groundwater pollution is a serious problem in the basin. At the regional scale, groundwater quality is threatened by man-made pollution from agricultural chemicals and by naturally occurring geological conditions such as elevated arsenic, fluoride, and uranium. Total dissolved solids, including pollutants, are most likely to rise in this shallow groundwater over time due to the continuous pumping-evaporation–infiltration cycle (CGWB, 2010; Deltares, 2018).

The quality of groundwater in the shallow aquifer is deteriorated by the vertical leakage of wastewater derived from anthropogenic sources (irrigation return flow, animal waste accumulation, domestic sewage water) and the nitrification process. Hence, management programs, such as periodic groundwater quality monitoring and awareness programs, will help preserve the groundwater resources in the shallow aquifer (Rajmohan, 2020).

There were several studies done in the past looking at the hazards of nitrate pollution of groundwater from non-point sources in agriculture, which examined the correlation between fertilizer use and nitrogenous pollution of groundwater using data that are spatial (Agrawal et al., 1999), temporal (Dutta et al., 2018) and both spatial and temporal (Sarkar et al., 2021). Within these, the influence of land use in determining nitrate contamination of river water (Santy et al., 2020) and geological formation characteristics on groundwater pollution (Sarkar et al., 2021) was also examined. The maximum nitrate levels reported in some groundwater samples from Haryana, Punjab, and Uttar Pradesh in the north, Tamil Nadu and Karnataka in the south, Orissa (Ganjam district) and Bihar in the east, and Gujarat in the west, also parallel high average nitrate and high N fertilizer consumption (Agrawal et al., 1999).

As noted by Dutta et al. (2018), the level of nitrate and phosphate use in agriculture has increased during the 16-year period (1999–2015) from 11,600 to 15,600 metric tons. The tonnages of manufactured fertilizer nutrients such as nitrate used in India in recent years show that the use of nitrate fertilizer has increased from roughly 2 million tons in 1970–1971 to 8 million tons in 1991–1992 (Agrawal et al., 1999). The concentration of nitrate in groundwater showed the same trend from 1999 to 2015 (Dutta et al., 2018).

Sarkar et al. (2021) statistically analyzed the nationwide distribution and 8-year temporal trends in groundwater nitrate and identified the occurrence and clustering of nitrate concentrations above the permissible limit of 45 mg/L using a large dataset. The distribution of groundwater nitrate indicated that 21 out of 36 states in India have elevated groundwater nitrate, and the majority of these states are from zones with high fertilizer applications. The study found that the majority of the administrative blocks with elevated levels of nitrate were in the alluvial Indo-Gangetic basin (IGB) aquifers and crystalline aquifers of the Indian cratonic region. The nitrate concentration was significantly higher in shallow wells than in deep wells. They also found that the highest percent of the blocks with nitrate concentrations exceeding permissible levels were located in the cropland areas. Clustering blocks with high groundwater nitrate in central, west, and north India coincided with extensive fertilizer usage in these areas.

Pollution of rivers, ponds, and lakes occurs due to agricultural runoff. The region is intensively farmed with a paddy-wheat system of cropping in Uttar Pradesh and Bihar and rice–rice in West Bengal. During the monsoon season, paddy is the most extensively cultivated crop. Gumma et al. (2020) estimate the total irrigated area in the Ganga basin (including Bangladesh) to be 44.689 m.ha, and the area under the rice–wheat system was estimated to be 11.666 m.ha, and that under rice–rice was estimated to be 5.52 m.ha (Gumma et al., 2019: Table 9.2). Of these, the entire rice–wheat area is in the Indian part of the Gangetic basin, and the rice–rice area is distributed between West Bengal and Bangladesh. Since paddy is grown under partially submerged conditions and the crop is also irrigated during dry spells in the kharif season, the unexpectedly heavy rainfall events during the season cause excessive runoff from the fields draining into the streams. Since the crop is heavily fertilized with nitrogenous fertilizers, the runoff water is also heavily polluted.

Another major source of nitrate pollution in surface water is intensive dairy farming. There are different degrees of intensification of dairy farming in the Ganga basin. The north-western part of the basin has benefited from the Green Revolution. The planting of high-yielding wheat and rice varieties, combined with the application of chemical fertilizers, resulted in much improved cereal production. The intensification of dairy production enabled by this was accompanied by a decrease in the ratio of draught animals to milk-producing animals and a more intensive use of water for growing fodder crops (Singh et al., 2004).

The dairy industry contributes to the production of large volumes of industrial wastewater with a high organic load that is difficult to remove. When compared with other food industry effluents, it has a high organic content, including high levels of carbohydrates and proteins. Organic compounds such as lactose, whey proteins, nutrients and fats emit foul odors, causing distress during the degradation process.

While water supply to industrial units by urban water utilities and other water supply agencies is metered in most cases, effluent discharge into the environment is regulated by the Water Pollution (control and prevention) Act. Industries complying with the effluent discharge norms prescribed in the consent under the Water Act by the State Pollution Control Boards/Pollution Control Committees (SPCBs/PCCs) are allowed to discharge treated effluent into the environment. The Government of India has stipulated general discharge standards and industry-specific effluent discharge standards under the Environment (Protection) Rules, 1986, with the aim of preventing pollution of water bodies. SPCBs/PCCs also identify and accordingly specify the outlets for discharge of treated effluent.

Legal action is normally initiated against the industries that discharge effluents into the environment only if the receiving water bodies or land are polluted as per the standards and norms set by the Pollution Control Agency or if the industries do not comply with the standards and norms set by the Envirornmental Protection Rules (EPA, 1995), while discharging their effluent into the environment.

However, the penalties imposed on industries and decisions on their ‘closure’ have nothing to do with the actual pollution load. On the contrary, they are based on whether or not: (i) the concentration of pollutants in the effluent exceeds the limits set by Environmental Pollution Regulations; and (ii) the existing norms with regard to the water quality indicators for the rivers/lakes are violated. The use of such blanket regulations provides no incentive for industries to reduce the aggregate pollution load from the discharged effluent unless and until the standards and norms for water quality in the river/lake to which the effluent is discharged are violated. As is evident, in regions with high ecological carrying capacity, the policy would give enough leeway for industries to discharge a high level of pollution load with the effluents, if the effluent quality is not monitored by the pollution control board.

Furthermore, the urban utilities are not under any legal obligation to comply with the effluent discharge norms for pollution control, and hence there is no mandatory compliance from their side.

Since the financial burden created by any investment in sewage treatment will have to be ultimately passed on to urban water users, which in turn will increase the water charges, and there is also a political compulsion to keep the water tariffs low and affordable, the full cost of sewerage treatment is seldom recovered by the urban water utilities. The small municipalities that are cash-starved do not show any special interest in setting up and running wastewater treatment systems. Nor are they held accountable for river or lake pollution by the state governments. The big municipalities and corporations do invest in treatment plants when funds are available from the Union Government. But there is no special incentive to run the plants properly to keep the pollution levels of water bodies low and within permissible levels, in the absence of a rewarding mechanism for keeping the water bodies (here, rivers) clean, and penalties for polluting. The high cost of plant operation and the lack of clear incentives to properly treat the wastewater are two major reasons for the improper running of sewage treatment plants in several urban areas.

Most of the polluting industries in the Ganga basin are quite small. It is impossible for small-scale industries to set up their own treatment plants. It is extremely difficult for the Pollution Control Board to monitor the activities of such units, as they are numerous and dispersed. Table 5 provides the statistics of the number of polluting industries that are registered in the Ganga Basin state-wise, the volume of water they consume, and the volume of wastewater they generate. Table 6 provides similar statistics category-wise, and these are all small-scale units. Of the 764 such units, 687 are in Uttar Pradesh. Furthermore, 444 out of the 764 are tanneries, all located in Kanpur. The average volume of water consumed by one tannery is just 65,000 L/day, and the average wastewater generated is 50,000 L/day. The highest water-consuming and wastewater-generating industry is the pulp and paper industry, whose average water consumption and wastewater generation per unit are 4,450 and 3000 m³/day, respectively.

The problem becomes larger if such SMEs are unregistered and operating illegally. Under such a scenario, for such small-scale units, the only option is to organize them, get them registered, and collect their effluent to be treated at a common effluent treatment plant (CETPs). However, such CETPs will only be viable if all the industries from which they have to collect the effluent carry the same type of pollutants. So meeting all these conditions is an insurmountable challenge. The current focus of the regulatory bodies is mainly on medium and large industries and their compliance with pollution control norms, where monitoring and enforcement are relatively easy.

The governments have not yet started looking at the problem of non-point pollution from agriculture with the seriousness it deserves. Currently, there are no mechanisms available to control or regulate the use of fertilizers and pesticides in agriculture or to restrict the pollution of groundwater or streams, except banning certain pesticides. Regulating pollution of groundwater and rivers caused by agricultural practices is challenging from both scientific and institutional points of view. On the institutional front, it is difficult to find out who applies fertilizers and how much, and whose actions have caused the pollution, even with continual monitoring of water quality for pesticide and fertilizer pollution. On the scientific front, it is difficult to assess what level of fertilizer and pesticide use can cause contamination of groundwater, as its vulnerability to pollution is a function of crop type, soil type, rainfall and depth to the groundwater table. Unless the permissible levels of fertilizer and pesticide use in a given locality are determined, it is difficult to develop evidence-based norms for pollution control.

An issue posing a big challenge to future investments in wastewater treatment is the poor economic viability of wastewater treatment (Bassi et al., 2022; Kumar & Tortajada, 2020). One of the benefits that can be derived from wastewater treatment is the use of treated wastewater for economic activities. In the case of the Ganga basin, agriculture is a major economic activity that can benefit from treated wastewater. However, scarcity of irrigation water is not a major issue for most parts of the Ganga River Basin owing to the abundant groundwater resources available and the high rainfall. Though the southern parts (in Madhya Pradesh) and eastern parts (in eastern Rajasthan and southern Haryana) do face water shortages, only the eastern parts of Rajasthan and parts of Haryana falling in the basin face pollution problems, and therefore wastewater for treatment and reuse would be available only in the eastern parts of Rajasthan and Haryana. If the treated water has to be taken to the areas in Madhya Pradesh, it would involve a long conveyance system and expensive pumping requirements, making them unviable.

Another potential (direct) benefit can be from treating wastewater to a potable level and supplying it for drinking, so as to save on the cost of freshwater supply. However, this option only makes economic sense if the cost of production and supply of good-quality water through this process is lower than the cost of production and supply of drinking water from underground sources. This is unlikely to be the case in most situations, especially in regions with abundant water resources. As the analysis by Kumar (2014) for 301 cities and towns shows, the cost of production and supply of water for urban water supply in water-rich regions is relatively low, and vice versa. Therefore, the direct benefits of wastewater treatment for drinking water only make sense in water-poor regions.

Even when the direct benefits are low, governments can invest in wastewater treatment systems provided there are sufficient social and environmental benefits (Kumar & Tortajada, 2020). The social benefits can be from positive public health outcomes owing to reduced degradation of drinking water sources or reduced contamination of irrigation water. The environmental benefits can be in the form of improvements in ecosystem health and the esthetic value of land and water. However, assessing the indirect benefits of WWT systems is challenging as it would require characterizing water use and reuse systems and socio-economic systems that depend on the water systems for social, economic and environmental uses. That said, indirect benefits are likely to be greater in regions that experience physical scarcity of water and environmental water stress, or in regions with low ecosystem carrying capacity. Such benefits will also be greater in high-income localities (Bassi et al., 2022).

In most parts of the Ganga River Basin, the social benefits associated with wastewater treatment are low because of the comparatively low cost of creating an alternate source of water for drinking and irrigation owing to the presence of abundant freshwater available in the basin (Kumar & Tortajada, 2020). As the environmental water stress in the basin is mostly confined to certain pockets, the aggregate ecological benefits of treating the wastewater before reuse in irrigated fields or disposal into streams are also likely to be high in such areas.

Given the large size of the regional aquifer and the intensive and extensive irrigated agriculture within the basin, there is a significant threat of ‘groundwater pollution’. It is difficult for a country like India to have a blanket approach for controlling groundwater pollution throughout the entire basin area involving measures that can directly impact the livelihoods of several millions of farmers. Therefore, it is important to adopt a risk assessment approach (Kumar et al., 2022).

As regards the risk, there is a need to systematically look at three dimensions: hazard, exposure, and vulnerability. In terms of hazard, it is a function of how intensive the crop production using fertilizers and pesticides is, how intensive dairy production is, and the level of fertilizer/pesticide use per unit area (Agrawal et al., 1999; Sarkar et al., 2021).

The exposure of the aquifers to pollution from leaching will depend on the rainfall conditions, the extent of irrigation that the crops receive, the soil hydraulic properties, and the geohydrological environment, such as the depth of the water table (Gerba et al., 1975). The higher the hydraulic conductivity (in light soils), the higher the exposure. The lower the depth of the water table, the higher the exposure will be (Gerba et al., 1975; Fraters et al., 2021). Fractured formations (Gerba et al., 1975) and fissured rocks (Franceys et al., 1992) will provide greater exposure (Gerba et al., 1975).

Vulnerability will depend on the extent to which groundwater is being tapped for human and animal consumption and the extent to which the raw groundwater is treated. If the water for drinking water supply is obtained from a deep, confined aquifer, then the ‘vulnerability’ of the communities to groundwater pollution can be considered nil.

That said, the conditions are favorable for the high groundwater pollution risk induced by agriculture in large areas, owing to intensive paddy cultivation, a shallow groundwater table, light soils, and a heavy reliance on untreated groundwater for drinking water supplies by communities. The high-risk areas of the Ganga basin need to be mapped, and the measures for reducing Nonpoint source (NPS) pollution of groundwater that are technical and institutional in nature need to be focused on such areas.

Similarly, high-risk zones for river pollution also need to be identified based on the flow regimes and the external and internal factors affecting pollution (discharge of effluents, climatic conditions, discharge of polluted groundwater into the river streams, etc.).

Unlike what is being done in developed countries such as the Netherlands (Fraters et al., 2021), Indian states cannot afford to levy on farmers who excessively use fertilizers and pesticides (in terms of dosage per unit area) and who keep livestock on their farms, given the larger concerns of food and nutritional security. While intensive crop cultivation and dairy farming do induce negative externalities in the environment and society, they also produce several positive welfare effects in the form of lowering food prices and creating employment opportunities in rural areas. What is required is a system of incentives and disincentives in the most vulnerable areas. Those who limit the use of fertilizers and pesticides and limit the number of animals (per unit size of the farm-holding) to the minimum permissible levels need to be rewarded through cash incentives. However, the challenge here is to work out the quantitative criteria and norms for chemical fertilizer and pesticide use and livestock keeping on farms to be accepted as ‘permissible’. The limits to be fixed should be based on scientific rationale. A levy can be imposed on those who exceed the limits set for fertilizers, pesticides, and animal holding.

In the Ganga River Basin, groundwater draft significantly impacts stream flows, particularly in the lean season. Such alterations in the flows have major implications for the pollution assimilation capacity of rivers and streams. However, the many millions of wells in the basin that draw water are owned by smallholder, low-income farmers. It is institutionally challenging to monitor and impose any control on their withdrawal. However, it is easy to identify private bulk water users who pump groundwater, such as large industries, as they are registered with the regulatory agencies. They will not have any difficulty paying for the resource. Industries that draw water from public reservoirs typically pay high water access fees to water resources departments. Hence, it is better and easier to target some of the bulk water users. A tax can be levied on these bulk water users to cover the costs of the resource. Such levies can be raised to cover the resource degradation cost if industries discharge the effluent on land or into water bodies.

The community's access to alternate sources of water in urban areas is one major factor limiting the ability of the water utilities to raise water tariffs in urban areas to achieve conservation and recover the rising cost of water supply. Urban dwellers in rich and middle-class localities do own wells operated by housing societies, which they use to augment the supplies from the municipalities. Often, they obtain water for domestic use from private tankers. It is only in poor localities and slums where urban dwellers are entirely dependent on municipal water supplies. This means that if the water tariffs are increased to cover the cost of production and supply, communities that can afford to pay for water might switch over to alternative sources or even refuse to pay for water collected from municipal services. This tendency limits the institutional capacity of urban water utilities. Hence, the best approach will be to seal wells owned by private individuals and housing societies.

One major impediment to sustainable investments in wastewater treatment is a lack of resources to meet capital and O&M costs. Currently, most of the capital investments for wastewater treatment being made by urban local bodies are funded by Central Assistance under the National River Conservation Plan. But this model is not self-sustaining. While the capital cost is covered by central funds, the cost of operation and maintenance of the system must be borne by the urban local body. The annual O&M costs for wastewater treatment systems are often quite high, at times exceeding the (annualized) capital cost (Kalbar et al., 2016; Kamble et al., 2019). It is therefore critical that these costs be added to the water supply cost as the ‘cost of resource degradation’ and levied from consumers. For efficient levying of such charges, the water supply to consumers must be metered, and pricing for water must be made volumetric. Once this is done, the urban water utilities or municipalities will be able to find resources to run the Sewage Treatment Plants (STPs) more efficiently.

Monitoring the activities of small-scale industries and enforcing regulations with regard to effluent discharge will be a herculean task, and would involve huge transaction costs. Therefore, it is advisable to introduce a pollution tax based on certain norms worked out separately for each type of industry based on the scale of operation. The revenue generated through this pollution tax collection can be used to set up CETPs. However, this is not an easy task. Clustering of industries, when industries that discharge the same type of effluent are located in the same area, will be required for this. This will require the relocation of many small-scale industries.

It is mandatory for large industrial units to comply with the effluent discharge standards set by the State Pollution Control Boards. Tax incentives can be offered to large, tax-paying industries that are willing to invest in technologies and systems to treat wastewater to quality standards higher than what is required by the policy in terms of effluent discharge norms, and to reuse it even when the policy does not demand such measures. This will encourage industries to go far beyond the basic minimum for regulatory compliance. The tax incentive can take the form of a percentage reduction in taxes proportional to the reduction in pollution levels achieved by the industry, below the maximum permissible levels for various pollutants or water quality indicators.

The problems of river pollution at any given location and time are not merely a function of the pollution load in the effluent discharged, but also of the quantum of stream flows and their quality, which get altered by a number of factors. They are impoundment and diversion of water upstream, water releases from upstream reservoirs, groundwater discharge into the streams, the amount of pollutants in that groundwater, and stream flow alterations due to groundwater overdraft. Yet, most previous attempts to analyze water pollution in the Ganga River Basin focused on wastewater generation and pollution of water bodies in isolation and ignored the larger issues in water resource development, water allocation, water use, reuse, and management at the basin scale.

Analyses of the surface water quality of the Ganga River and its tributaries at various locations in the basin with respect to select chemical and biological parameters during two different time periods (2012 and 2020) reveal certain regional patterns. Serious water quality problems, with values of BOD, pH, nitrate, electrical conductivity, total coliform, and fecal coliform count exceeding permissible limits and low values of DO, are witnessed only in the western and south-western parts of the basin, including the parts falling in eastern Rajasthan, southern Haryana, the National Capital Region, and north-western Madhya Pradesh. While the quality of water generally improves in the eastern parts of the basin, it is quite good in the upper Ganga basin (in Uttarakhand). On a temporal scale, areas with high pH and high conductivity have increased, while areas with high BOD (7.0–21 mg/L) have decreased. Areas representing high DO content (5.0–9.8 mg/L) have also declined, while those with lower DO content (1.35–5.0 mg/L) have increased. Hence, future investments in wastewater treatment should focus on areas where the pollution problems are severe and where the benefits from wastewater treatment are likely to be high due to scarcity of water for competitive uses and environmental water stress.

That said, the Ganga River system cannot be said to be clean unless the pollution of the vast aquifers underlying the river system that are hydraulically interconnected with the river system and surface water flows is prevented. From an anthropocentric perspective, the problems of pollution in the Ganga River Basin cannot be solved unless the problem of groundwater pollution is remedied. Diffuse pollution from intensive agricultural activities, including dairy farming, is a serious problem in the Ganga basin, posing a significant threat to the extensive shallow aquifers underlying the basin, which supply drinking water to hundreds of millions of rural and urban households in the basin area. The runoff from cropland and dairy farms also pollutes the rivers. The intensive and extensive paddy cultivation in the basin, covering around 16–17 m· ha, poses the biggest challenge as paddy wetlands are a major source of groundwater recharge, and the deep-percolating water rich in nutrients contaminates the groundwater while replenishing it.

The existing approach to pollution control and water quality management suffers from several inadequacies. These are lack of incentive among the polluting industries and urban local bodies to reduce the pollution load; poor enforcement of pollution control regulations on small and dispersed industrial units due to the difficulty in monitoring; the absence of a mechanism for controlling non-point pollution from agriculture and dairy farming; and inadequate emphasis on the economic viability of wastewater treatment investments. That said, there are several measures that could, in the short term, be implemented to significantly reduce pollution in the Ganga Basin.

First, the areas that are most vulnerable from the point of view of ‘non-point pollution’ need to be identified. Cash incentives need to be provided to the crop and dairy farmers to reduce the nitrogen and phosphate load on land in such areas if they are able to limit the use of these nutrients on their agricultural land to a pre-determined level worked out on the basis of several factors that determine the groundwater pollution risk from agriculture. However, monitoring land use and livestock holdings will be an enormous task, given the several millions of farmers operating in the basin.

Furthermore, heavy-duty industrial water users should be taxed to cover the resource cost and the resource degradation cost. In urban areas where volumetric pricing of water is necessary to affect conservation behavior and cost recovery, the sealing of private wells used for drinking water supply in housing colonies should be made mandatory to bring down water consumption. Furthermore, urban local bodies must incorporate wastewater treatment costs into the water charges levied by them so that they are able to find additional resources to invest in STPs and run them efficiently. The hundreds of small-scale industries that cause serious pollution need to be taxed on the basis of some simple criteria to avoid the enormous transaction costs of monitoring and enforcement. The revenue generated through this can be used for investing in CETPs. At the same time, large industries whose environmental performance goes beyond compliance with effluent discharge norms and recycles treated wastewater should be offered tax incentives.

There is a lot of scope for research in the future that can help identify effective and sustainable interventions for pollution reduction in the Ganga River Basin. One of them is the identification of areas that are most susceptible to non-point pollution of groundwater and surface water bodies in the basin and where institutional measures for mitigation are most essential. Another area of research is understanding the degree of wastewater treatment that would be desirable in different parts of the basin and that would make wastewater treatment economically viable as well as ecologically sound.

To conclude, reducing pollution in the Ganga basin requires an integrated approach wherein the regions where water resources are scarce, environmental water scarcity is severe, and pollution levels are high, need to be focused. It should also consider the hydrological and ecological integrity of the basin and the economic viability of wastewater treatment options, which means giving due consideration to the quantum and pattern of surface water flows in different river stretches, the vulnerability of groundwater to pollution, and the dynamics of surface water–groundwater interactions. Furthermore, the cleaning of Ganga entails not only treating sewage and effluent but also preventing pollution of surface water bodies and groundwater. Non-point pollution of groundwater and surface water is as important as point pollution. Reducing pollution requires creating incentives and disincentives through market instruments and regulations. The basic aim of using such instruments is that efforts to conserve water and reduce pollution result in direct economic benefits. Only that can sustain the huge infrastructural investments made for clean the Ganga.

This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 821051 and by the Government of India through the Department of Biotechnology (DBT).

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.