Why in news?

An assessment of India’s groundwater by the Central Ground Water Board (CGWB) found that several States are grappling with a serious problem of nitrate contamination.

What’s in today’s article?

• Central Ground Water Board (CGWB)
• Excessive Nitrate in Groundwater: A Growing Concern
• Regional Analysis of Nitrate Contamination in Groundwater
• Other Major Chemical Contaminants in Groundwater
• State of Groundwater in 2024

Excessive Nitrate in Groundwater: A Growing Concern

• Increase in Nitrate-Contaminated Districts
  • The number of districts with excessive nitrate in groundwater increased from 359 in 2017 to 440 in 2023, impacting nearly 56% of India’s districts.
  • Excessive nitrate levels are defined as concentrations above 45 mg/l.
• Groundwater Testing and Trends
  • 2017 Findings: 13,028 samples were analyzed, with 21.6% showing excessive nitrate levels.
  • 2023 Findings: Of 15,239 samples tested, 19.8% had nitrate levels above safe limits.
  • While the percentage of affected samples has not substantially changed, the number of contaminated districts has risen.
• Health Concerns
  • Excessive nitrate in groundwater causes methemoglobinemia, reducing the ability of red blood cells to carry oxygen, particularly affecting infants and vulnerable populations.
• Environmental Impact
  • Elevated nitrate levels in groundwater can lead to algal blooms in lakes and ponds, severely degrading aquatic ecosystems by depleting oxygen and harming biodiversity.
• Sources of Nitrate Contamination
  • Agricultural Practices: Farmers use fertilizers such as ammonium nitrate, calcium nitrate, urea, and diammonium hydrogen phosphate, leading to nitrogen leaching into groundwater.
• Forms of Dissolved Nitrogen in Groundwater:
  • Nitrate (NO3-)
  • Ammonium (NH4+)
  • Ammonia (NH3)
  • Nitrite (NO2-)
  • Nitrogen gas (N2)
  • Nitrous oxide (N2O)
  • Organic nitrogen

Regional Analysis of Nitrate Contamination in Groundwater

• States with the Highest Proportion of Contaminated Blocks
  • Rajasthan: 49% of tested samples exceeded permissible nitrate levels.
  • Karnataka: 48% of tested samples were contaminated.
  • Tamil Nadu: 37% of tested samples showed excessive nitrate levels.
• States with Persistent Nitrate Issues
  • Rajasthan, Madhya Pradesh, and Gujarat: These states have had a long-standing nitrate problem with contamination levels remaining relatively constant since 2017.
• Emerging Nitrate Concerns in Central and Southern India
  • Increasing nitrate contamination has been observed in blocks in central and southern India, raising alarm.
  • States with notable levels of contamination:
    • Maharashtra: 35.74%
    • Telangana: 27.48%
    • Andhra Pradesh: 23.5%
    • Madhya Pradesh: 22.58%

Other Major Chemical Contaminants in Groundwater

• Key Contaminants
  • Arsenic, Iron, Fluoride, and Uranium: These chemicals significantly affect groundwater quality alongside nitrate contamination.
  • Fluoride Contamination: 9.04% of tested groundwater samples had fluoride levels exceeding the permissible limit.
    • High-Risk States: Rajasthan, Haryana, Karnataka, Andhra Pradesh, and Telangana reported high fluoride concentrations, making it a “major concern.”
  • Uranium Contamination: Several samples had uranium concentrations exceeding 100 ppb (parts per billion), far above the safe limit of 30 ppb.
    • High-Risk States: Rajasthan and Punjab reported the maximum number of contaminated samples. Other affected states include Gujarat, Haryana, Tamil Nadu, Andhra Pradesh, and Karnataka.
• Cause
  • Predominantly observed in regions with over-exploited groundwater (where water withdrawal exceeds replenishment).

State of Groundwater in 2024

• Groundwater Extraction: The country’s groundwater extraction rate stands at 60.4%, consistent since 2009.
• Safe Zones: Approximately 73% of blocks are classified as ‘safe,’ indicating sufficient replenishment to balance water withdrawal.

Central Ground Water Board (CGWB)

• About
  • The Central Groundwater Board (CGWB) is a key organization under India's Ministry of Jal Shakti, responsible for monitoring, managing, and regulating groundwater resources.
  • It maintains a vast network of observation wells to assess groundwater quality and availability.
  • It also provides technical guidance, promotes sustainable practices, and formulates policies to address groundwater-related challenges across the country.
• Head quarter - Bhujal Bhawan, Faridabad, Haryana
• Organization Setup: The Board is headed by the Chairman and has five members.
• Measurement of Groundwater Levels: Observation Network
  • Current Network: The Central Ground Water Board (CGWB) uses 26,000 observation wells to manually measure groundwater levels.
  • Digital Integration: Since 2023, 16,000-17,000 piezometers equipped with digital water level recorders transmit real-time data to a central system.