It evolves a methodology for identifying hot spots in Indian rivers. The water quality data is based on the average values observed during the last ten years (2001-2011) at 371 monitoring stations of CWC on almost all major, medium and minor rivers in India. In respect of Dissolved Oxygen and Biochemical Oxygen Demand, the Central Pollution Control Board's classification has been considered for evaluating the hot spot in the rivers.

The physical and chemical quality of river water is important in deciding its suitability for drinking purposes. As such the suitability of river water for potable uses with regard to its chemical quality has to be deciphered and defined on the basis of the some vital characteristics of the water. Bureau of Indian Standards (BIS) vide its document IS: 10500:1991, edition 2.2 (2003‐09) has recommended the quality standards for drinking water and these have been used for finding the suitability of river water. On this basis of classification, the natural river water of India has been categorized as desirable, permissible and unfit for human consumption.

River water quality is highly variable by nature due to environmental conditions such as basin lithology, vegetation and climate. In small watersheds spatial variations extend over orders of magnitude for most major elements and nutrients, while this variability is an order of magnitude lower for major basins. Standard river water for use as reference is therefore not applicable.

The river systems that have been included in the report include - Indus, Brahmaputra, Ganga, Yamuna, Narmada, Tapti, Godavari, Krishna, Kaveri and Mahanadi. The physico‐chemical parameters like pH, electrical conductance, Total Dissolved Solids (TDS), Chloride, Fluoride, Iron, Nitrate, Sulphate, Total Hardness, Calcium and Magnesium are the main constituents defining the quality of river water in surface water. Therefore, presence of these parameters in river water beyond the permissible limit in the absence of alternate source has been considered as river water quality hotspots.

River water quality hot spot tables of the rivers have been prepared depicting the main parameters mentioned above based on their distribution –

• Water quality sites in the following rivers have pH value above 8.5 - Sindh, Rind, Dhasan, Parwati, Parwan, Kalisind, Pranhita, Ponniyar, Gomti, Tungabhadra and Sankh. Gummanur water quality station in Ponniyar river in Dharmapuri, Tamil Nadu was reported to have the highest monsoon and non-monsoon pH values of 9.91 and 8.78 respectively.
• Stations having electrical conductance (EC) > 3000 micro-siemens/cm were – Elunuthimangalam, Erode in Noyyal river basin (5910 – monsoon, 4602 – non monsoon), Tal, Ratlam in Chambal river basin (4062 – monsoon) and Vautha, Kheda in Sabarmati basin (3409 – non monsoon).
• Elunuthimangalam water quality station in Erode, Noyyal river basin in Tamil Nadu has magnesium concentration above 100 mg/l [104.70 - monsoon].
• The stations having Total Hardness (TH) concentration above 600 mg/l in river water are – Tal, Ratlam in Chambal river (624 - monsoon) and Elunuthimangalam, Coimbatore in Noyyal river basin in Erode, Noyyal basin (684 – monsoon and 656 – non monsoon).
• The water quality station at Elunuthimangalam, Erode, Noyyal river basin has Chloride concentration above 1000 mg/l (1656 – monsoon and 1175 – non monsoon).
• The water quality station at Tal, Ratlam in Chambal river basin has Sulphate concentration above 400 mg/l in river (672 – non monsoon).
• All the water quality stations of CWC have nitrate and arsenic concentration within the permissible limits.
• There are twenty two stations having Iron (Fe) concentration above 1.0 mg/l in river. The highest recorded iron concentration was in Kumhhari water quality station at Balaghat in Wainganga river basin (16.40 – monsoon, 64.39 – non monsoon). Of the twenty two stations eleven were in Bihar-Jharkhand on the Ganga, Sone, Koel, North Koel, Phalgu, Punpun and Gandak rivers.
• Fifteen water quality stations were recorded as having Fluoride concentration above 1.5 mg/l,  the highest being in Thimmanahalli, Hassan in Yagachi river basin in Karnataka (4.08 - monsoon and 5.07 – non monsoon).
• Seventeen stations recorded Dissolved Oxygen concentration below 5.0 mg/l in river water. More alarming concentrations were recorded mostly in Orissa and Chhattisgarh – Darrighat, Bilaspur in Mahanadi basin (0.8 – monsoon, 0.9 – non monsoon), MBPL, Bilaspur in Hasdeo basin (0.3 – monsoon, 0.5 – non monsoon) and Baridhinala, Paschim Singbhum in Subarnarekha river basin (0.8 - monsoon and 0.9 – non monsoon).
• Thirty six water quality stations had Biochemical Oxygen Demand concentration above 3.0 mg/l in river water. Very high concentrations were recorded in Darrighat, Bilaspur in Arpa basin (241.6 – monsoon and 282.4 – non monsoon) and MBPL, Bilaspur in Hasdeo basin (276.3 – monsoon, 259.8 – non monsoon). Thirteen water quality stations in the Yamuna river and its tributaries (Betwa, Hindon, Sindh, Dhasan and Parwati) recorded very high concentrations of BOD.

The report is structured as follows:

• Chapter 1: Introduction
• Chapter 2: Water resources in India at a glance
• Chapter 3: Indian river system
• Chapter 4: Hydrochemistry: Chemistry of rain water, surface water and ground water
• Chapter 5: River water monitoring in CWC
• Chapter 6: River water pollution
• Chapter 7: River water quality hot spots of India: pH (Hydrogen Ion Concentration), Electrical Conductance (Salinity), Chloride, Fluoride, Nitrate, Sulphate, Iron, Calcium, Magnesium, Total Hardness, Dissolved Oxygen, Bio-Chemical Oxygen Demand, Total Coliforms and Fecal Coliforms, Arsenic

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