Block-Level Assessment, Soil Profile and Research Compilation
CGWB 2022 (district classifications) · Updated through 2025
Bihar sits astride one of the world's largest alluvial aquifer systems in the north and hard-rock terrain in the south. The state is classified "Safe" in aggregate - confirmed across CGWB assessments from 2022 through 2025 - yet significant intra-state disparities mask critical stress in 13 of 38 districts. The CGWB 2025 assessment cites Bihar among states showing significant groundwater recharge increase, though the 2024 assessment recorded a 0.32 BCM decline in net availability compared to 2023, driven by below-normal kharif rainfall in South Bihar.
Agriculture accounts for approximately 87% of groundwater extraction in Bihar. Paddy cultivation during kharif - especially in water-stressed South Bihar - drives peak draft. Diesel pump sets (4.2 million) are the primary lifting mechanism, with less than 18% coverage by canal irrigation.
Geogenic arsenic contamination at concentrations above 10 ppb (WHO guideline) has been confirmed in 12 districts, principally along the Ganga alluvial belt: Patna, Saran, Vaishali, Samastipur, Bhagalpur, Khagaria and Bhojpur. High-As groundwater is the sole drinking source in many villages.
CGWB Bihar Water Level Bulletin (May 2025, 804 dug wells): depths range from 0.9 m (Nalanda) to 16.8 m (Bhagalpur). Distribution: 3% of wells below 2 m, 43% at 2 to 5 m, 51% at 5 to 10 m, 3% deeper than 10 m. Kaimur, Rohtas and Nalanda show a rise of over 4 m in some monitored wells - a positive recharge signal. Saran, Muzaffarpur, Gaya, Nawada and Samastipur continue to show seasonal decline of up to 2 m.
Bihar has 892 monitored observation wells across 38 districts. Of these, 312 are National Hydrograph Network (NHN) stations with quarterly readings. Real-time telemetry covers only 64 wells as of 2024, highlighting a critical gap in block-level data density for timely groundwater governance.
Bihar's hydrogeology divides sharply at the Ganga river corridor. The vast Indo-Gangetic Alluvial Plain (North Bihar) holds multi-layered unconsolidated aquifers with enormous storage potential, while the Chotanagpur Plateau fringe (South Bihar) presents hard-rock terrain with limited, localized groundwater occurrence.
A discontinuous layer of calcium carbonate nodules (kankar) occurs at 1 to 5 m depth in the central Gangetic plains. This layer restricts vertical percolation in some areas but also acts as a shallow aquiclude protecting deeper aquifers from surface contamination. Well screens must be positioned below this layer for reliable yields in districts like Patna, Vaishali and Bhojpur.
The Terai belt along the Nepal border (West and East Champaran, Sitamarhi, Sheohar, Madhubani) receives the highest rainfall in Bihar (1,300 to 1,600 mm/year) and maintains the most vigorous aquifer recharge. Water tables are often within 2 to 4 m of the surface post-monsoon. This zone is Bihar's strategic groundwater reserve and must be protected from over-extraction.
Choropleth map showing district-level stage of groundwater development (annual draft as percentage of annual extractable resource) across all 38 Bihar districts. District classifications are from the CGWB National Compilation 2022 - the most granular publicly available block-level assessment. The CGWB 2025 national assessment confirms Bihar's aggregate Safe status. Hover or tap any district for depth and trend data.
District and block classifications are sourced from the CGWB National Compilation 2022 - the most recent publicly available assessment with district-level resolution for Bihar. A Bihar state-specific 2024 report (CGWB) exists but is not yet publicly disaggregated to block level in accessible form. Of 534 administrative blocks, 23 are over-exploited or critical - concentrated in South Bihar and the Patna-Bhojpur corridor.
| District | Key Stressed Blocks | Status | Stage % | Pre-monsoon Depth (m) | Post-monsoon Depth (m) | Decadal Trend (m/yr) | Primary Stress Driver |
|---|---|---|---|---|---|---|---|
| Rohtas | Dawath, Nokha, Chenari, Kochas, Dinara, Sasaram (T) | Over-exploited | 118% | 14.2 | 6.1 | -1.48 | Rabi irrigation; wheat + potato + vegetable chains; 6-month growing season |
| Gaya | Amas, Belaganj, Guraru, Tikari, Atri, Dobhi | Critical | 95% | 12.8 | 5.8 | -1.21 | Hard-rock terrain; limited recharge; paddy irrigation; urban demand (Gaya city) |
| Nalanda | Ben, Hilsa, Noorsarai, Rajgir, Islampur, Bind | Critical | 92% | 11.4 | 5.2 | -0.98 | Vegetable cultivation (high water demand); hard-rock aquifer; low recharge |
| Jehanabad | Makhdumpur, Kako, Hulasganj | Critical | 91% | 10.9 | 5.0 | -0.87 | Limited aquifer storage; sugarcane belt; transition zone geology |
| Patna | Khusrupur, Naubatpur, Bihta, Bikram, Dulhin Bazar | Semi-critical | 84% | 9.6 | 4.2 | -0.72 | High urban demand (Patna city); peri-urban agriculture; industrial use |
| Bhojpur | Agiaon, Sandesh, Udwantnagar, Barhara, Piro | Semi-critical | 81% | 8.8 | 4.0 | -0.61 | Wheat-rice rotation; intensive groundwater irrigation |
| Buxar | Simri, Buxar (T), Rajpur, Chausa | Semi-critical | 78% | 8.1 | 3.6 | -0.55 | Rabi wheat; Son river plain; moderate hard-rock influence in south |
| Kaimur (Bhabua) | Chainpur, Mohania, Kudra, Adhaura | Semi-critical | 77% | 10.2 | 4.8 | -0.68 | Hard-rock + alluvial transition; Kaimur plateau; irrigation-driven |
| Aurangabad | Daudnagar, Obra, Rafiganj, Goh, Haspura | Semi-critical | 75% | 11.1 | 5.3 | -0.74 | Rocky terrain; limited recharge area; high irrigation demand |
| Nawada | Nawada (T), Hisua, Warsaliganj, Rajauli | Semi-critical | 73% | 9.8 | 4.9 | -0.62 | Plateau fringe; thin weathered zone; seasonal streams only |
| Munger | Tarapur, Jamalpur, Haveli Kharagpur, Dharhara | Semi-critical | 72% | 7.9 | 3.5 | -0.48 | Ganga-Son doab; riverine sandy aquifer; high paddy extraction |
| Begusarai | Matihani, Begusarai (T), Balia, Sahebpur Kamal | Semi-critical | 71% | 6.8 | 2.9 | -0.42 | Industrial zone (BPCL, HPCL refineries); peri-urban extraction; paddy belt |
| Sheikhpura | Sheikhpura (T), Barbigha, Shekhopur Sarai | Semi-critical | 70% | 8.4 | 3.8 | -0.44 | Small district; high per-area extraction; transition geology |
| Muzaffarpur | Saraiya, Paroo, Musahari, Kanti - all Safe | Safe | 56% | 4.8 | 2.1 | -0.16 | Gandak alluvial; strong recharge; managed extraction |
| Samastipur | Pusa, Morwa, Warisnagar, Singhia - all Safe | Safe | 62% | 4.9 | 2.2 | -0.18 | Burhi Gandak alluvial plain; good recharge; RPCAU area |
| Vaishali | Bidupur, Mahua, Raghopur - all Safe | Safe | 63% | 5.2 | 2.4 | -0.20 | Gandak floodplain; strong seasonal recharge |
(T) = Town/municipal area | Depth to water table in metres below ground level | Source: CGWB National Compilation 2022, BWRD Monitoring Reports 2023-24
Soil characteristics directly control groundwater recharge rates, irrigation demand, and contamination pathways. Bihar is divided into four soil-hydrological zones based on parent material, texture, drainage characteristics and groundwater interaction.
Pre-monsoon water table depth (depth to groundwater in metres below ground level) provides the most reliable indicator of groundwater stress. Districts are ranked below from deepest (most stressed) to shallowest (most secure), alongside key quality parameters.
Groundwater Quality Parameters
Based on CGWB district classifications (2022), CGWB national assessments 2023 to 2025, CGWB Bihar Pre-monsoon Bulletin May 2025, and BWRD monitoring data. The CGWB 2025 assessment confirms Bihar's Safe aggregate status and notes significant recharge improvement; however, stressed districts require sustained intervention. The Groundwater (Development and Management) Act 2020 and PMKSY-Per Drop More Crop scheme provide the legislative and financial instruments for most actions below.
Rohtas is Bihar's only over-exploited district (118% stage). A district-level Groundwater Authority must be notified immediately under the Groundwater (Development and Management) Act 2020. A permit system for new dug-wells and bore-wells must be enforced. Existing high-density tubewell areas (Dawath, Nokha, Kochas blocks) should be designated as Groundwater Conservation Zones with mandatory metered extraction. The 2023 crop season exacerbated decline by 0.8 m in just four months.
All three critical districts require immediate Aquifer Mapping (CGWB NAtional Aquifer Management Programme, NAQUIM) at 1:50,000 scale to delineate recharge zones and stressed blocks precisely. Mandatory micro-irrigation (drip/sprinkler) for paddy under PM Krishi Sinchayee Yojana should be enforced for holdings above 2 hectares. Rooftop rainwater harvesting on public and commercial buildings must be legally mandated within 12 months of notification.
An estimated 6.8 million people in 12 Bihar districts draw drinking water from arsenic-affected shallow tubewells. PHED should accelerate installation of community-scale Arsenic Removal and Safe Piped Water (ARSP) systems under Jal Jeevan Mission for all habitations where As >10 ppb is confirmed. Simultaneously, deep aquifer (100 m plus) tubewells that tap pre-contamination strata should be installed in arsenic-affected panchayats, as these aquifers are consistently arsenic-free.
South Bihar's hard-rock terrain and low-infiltration lateritic soils produce high runoff. Under PMKSY-Watershed Development Component, at least 2,800 check dams, farm ponds, percolation tanks and nala-bunding structures should be constructed across Rohtas, Kaimur, Gaya, Aurangabad, Nawada and Nalanda by 2027. NABARD's Watershed Development Fund offers a dedicated financing window. Each structure should be linked to a CGWB-monitored observation well to measure recharge impact.
Nine semi-critical districts (Patna, Bhojpur, Buxar, Kaimur, Aurangabad, Nawada, Munger, Begusarai, Sheikhpura) together account for approximately 28% of Bihar's groundwater draft. A targeted subsidy-plus-credit package through ATMA and NABARD should make drip and sprinkler irrigation economically dominant in these districts within three years. Wheat and vegetable cultivation in Bhojpur-Buxar should shift from flood irrigation to sprinkler by incentivizing certified water-efficient cultivars.
Bihar currently monitors only 892 observation wells for 38 districts and 534 blocks - a density of 1.7 wells per block. This is inadequate for block-level governance. CGWB and BWRD should jointly deploy IoT-enabled automated water-level recorders (DWLRs) to achieve a minimum of 5 monitored wells per block in stressed districts, rising to 3 per block state-wide, within 36 months. Integration with INDIA-WRIS real-time portal and state GIS dashboard is essential for agro-advisory and regulation.
The Terai belt (West and East Champaran, Sitamarhi, Sheohar, Madhubani) represents Bihar's largest groundwater reserve with extraction stages below 50%. Proactive land-use zoning must prevent this belt from sliding into semi-critical status as agricultural intensification and urban growth expand northward. A Bihar Groundwater Reserve Zone (BGRZ) should be legally notified, restricting tube-well density and mandating recharge structures for any new commercial extraction. This is Bihar's strategic groundwater insurance for the next generation.
District-level stage of development (Plates III-IV) uses CGWB 2022 - the most granular publicly available block-level classification. The 2023-2025 national assessments confirm Bihar's aggregate Safe status; district disaggregation is not publicly released at equivalent resolution in those cycles.