How Bihar’s groundwater filters fail the people who need them most

In Bihar, water runs deep, but not always clean. Almost every home in the state depends on groundwater for drinking, cooking, and daily needs. But for millions of families, every sip carries a hidden risk of contamination by arsenic, iron, or fluoride.

To tackle this, the state’s Public Health Engineering Department (PHED) has been installing thousands of groundwater “remediation units”, systems designed to filter out these toxins and provide safe water. But a recent study led by Ajmal Roshan and colleagues paints a worrying picture: these filters are not always placed where contamination is worst.

The research ‘Comparison of the distribution of groundwater remediation units and contaminant (arsenic, iron, fluoride) distribution in Bihar, India for improved water security and management’, published in the Journal of Environmental Management, compares where Bihar’s Public Health Engineering Department (PHED) installed remediation systems with actual contaminant distribution data from a state-wide groundwater survey. The result? Stark mismatches between the technology’s reach and the regions facing the gravest risks.

The toxic trio: Arsenic, iron, and fluoride

Bihar’s groundwater faces three main natural pollutants, each with serious health effects.

• Arsenic is the most dangerous. It’s invisible, tasteless, and linked to cancers, heart disease, and skin disorders. Between 1 million and 21 million people in Bihar could be drinking water with unsafe arsenic levels.

• Iron, though less deadly, turns water reddish and foul-smelling. It exceeds safe limits (0.3 mg/L as per BIS) in many areas and can even worsen arsenic exposure by releasing more of it from the soil.

• Fluoride, found mostly in southern Bihar’s rocky terrain, causes dental and skeletal fluorosis — discoloured teeth and brittle bones that can make life painful for years.

Together, these pollutants silently damage public health, productivity, and well-being across the state.

Where the filters are, and where they’re not

Bihar has 8,406 panchayats, and about 3,083 (37%) have at least one remediation unit. But the spread is uneven.

• Arsenic units: 581 panchayats (mostly along the Ganga belt)

• Iron units: 1,604 panchayats (mostly in the north-east)

• Fluoride units: 788 panchayats (mostly in the south)
  

Let’s break that down further.

Arsenic filters hug the Ganga:

Most arsenic treatment units are in 14 districts along the Ganga — Patna, Bhagalpur, Begusarai, and others. Over 60 percent are within 10 km of the river, even though only 10 percent of Bihar’s villages are that close.

This makes sense historically, since arsenic contamination was first discovered near the river. But new surveys show that arsenic has spread inland to districts like Madhubani, Supaul, and West Champaran, where almost no units exist. In short, while the Ganga belt is saturated with filters, large inland areas remain dangerously exposed.

Iron filters cluster in the north-east:

Almost all iron remediation units are found in 11 districts in the Kosi–Seemanchal belt — Araria, Katihar, Kishanganj, and Purnea. But high iron levels have also been reported in Buxar, Sitamarhi, and Gopalganj, where no units were installed.

The response is geographically narrow and strong in the north-east, missing in central and western Bihar.

Fluoride filters stay south of the Ganga:

Fluoride filters are concentrated in the southern districts — Gaya, Jamui, Nalanda, and Rohtas. These are indeed known fluoride zones, but the study found that some of these places now have safe levels, while other emerging hotspots were left out entirely.

No fluoride filters exist north of the Ganga, even though newer tests have detected fluoride pockets there too.

1. Arsenic (As) Remediation Units

• Geographic spread: Installed in 14 districts—Begusarai, Bhagalpur, Bhojpur, Buxar, Darbhanga, Katihar, Khagaria, Lakhisarai, Munger, Patna, Samastipur, Saran, Sitamarhi, and Vaishali.

• Spatial pattern: Most are located in the central belt of Bihar, aligned east–west along the River Ganges corridor. This alignment mirrors major transport routes and settlement clusters.

• River proximity bias:

  • Over 60% of all As units are located within 10 km of the Ganges, though only 10% of Bihar’s panchayats are that close.

  • Roughly 75% of As units are within 10 km of a major river, compared to only 30% of total panchayats.

• Implication: Yet arsenic contamination extends far beyond riverine districts, into northern Bihar—places like Madhubani, Supaul, and West Champaran, where the study found elevated arsenic levels but virtually no remediation units. Remediation efforts are concentrated along riverine areas, especially near the Ganges, leaving inland and upland regions with limited coverage, despite potential arsenic risks there. 

2. Iron (Fe) Remediation Units

• Geographic spread: Over 99 percent of iron units are confined to just 11 districts in eastern Bihar — Araria, Begusarai, Bhagalpur, Katihar, Khagaria, Kishanganj, Madhepura, Munger, Purnea, Saharsa, and Supaul. Still, excessive iron was recorded in districts such as Buxar, Sitamarhi, and Gopalganj, none of which received government units.

• Spatial pattern: Strong concentration in the northeastern part of Bihar, especially within the Kosi–Seemanchal belt (Araria, Kishanganj, Purnea, Katihar).

• Absence elsewhere: Apart from these northeastern districts, few other areas of Bihar have PHED-installed Fe remediation units, even though iron is a common groundwater contaminant statewide.

• Implication: The Fe response is geographically narrow, targeting regions with chronic iron issues but leaving central and southern districts largely uncovered.

3. Fluoride (F⁻) Remediation Units

• Geographic spread: Installed in 11 districts — Aurangabad, Banka, Bhagalpur, Gaya, Jamui, Kaimur, Munger, Nalanda, Nawada, Rohtas, and Sheikhpura.

• Spatial pattern: All fluoride remediation units are located south of the River Ganges, with no installations north of the river. True to historical data, most fluoride filters are in southern districts such as Gaya and Jamui. Yet the study’s statewide sampling showed fluoride levels within safe limits in many of these areas, raising questions about whether expensive installations were justified.

• Implication: This reflects the known fluoride belt of Bihar in the southern hard-rock and semi-arid districts but highlights regional exclusivity—areas north of the Ganga have been left out entirely. 

4. Key Observations

1. Clear contaminant-specific clustering:

   • Arsenic units → riverine, Ganges belt (central Bihar).

   • Iron units → northeastern Bihar (Kosi-Seemanchal).

   • Fluoride units → southern Bihar, south of the Ganga.

2. Bias towards accessible, river-adjacent panchayats: The siting of As units shows disproportionate proximity to the Ganges and major rivers, suggesting accessibility (roads, settlements, water sources) may have influenced PHED’s choices.

3. Unequal geographic coverage: Many districts with known contamination risks lack PHED-installed units, raising questions about equity in remediation planning.

4. Data integrity: Slight mismatches exist between PHED records and mapped data (due to missing shapefile entries), but the overall distribution pattern remains robust.

Bihar’s PHED remediation strategy is highly clustered — As units dominate the Ganga belt, Fe units are confined to the north-east, and F⁻ units sit south of the river. Coverage remains partial and geographically biassed, with significant gaps in inland and non-priority districts.

Why are the filters misplaced?

The study points to several reasons behind this mismatch.

1. Old and biased data

• Early testing in Bihar focused on villages near the Ganga, where arsenic was first found. Those areas became the “priority zones”. As a result, when PHED planned remediation, it relied on old maps and missed inland contamination that later surveys uncovered.

2. Conflicting contamination standards

• Different agencies use different safety limits. For arsenic, PHED labels an area “affected” only if levels exceed 50 µg/L, while the Central Ground Water Board (CGWB) follows the WHO guideline of 10 µg/L. That’s a fivefold difference — meaning PHED ends up declaring fewer districts as risky, leading to fewer installations.

3. Administrative convenience

• It’s easier and cheaper to install units near main roads or big villages than in remote areas with poor access. This logistical bias explains why river-adjacent panchayats have so many filters.

4. Slow rollouts

• Large schemes in India often move in phases. Bihar’s effort might expand later, but in the meantime, generations could be drinking contaminated water.

Human costs and local realities

The consequences of these mismatches are far from abstract. In Madhubani district, the study found that half of the groundwater samples exceeded WHO’s arsenic limit of 10 µg/L. Yet not a single arsenic remediation unit was reported there. In Buxar, 80 percent of samples breached the iron guideline, but the government has installed no iron units.

On the flip side, in Bhojpur and Bhagalpur, arsenic units are widespread—yet the researchers’ sampling found no exceedances in tested wells. Similar patterns were noted for fluoride units in Sheikhpura and Banka, where filters exist despite no violations recorded in the latest survey.

For affected families, the absence of safe water infrastructure means relying on contaminated sources, risking long-term illness. Conversely, misplaced units represent wasted public funds that could have saved lives elsewhere.

A call for smarter water security

The study does not dismiss the government’s efforts. In fact, Bihar has made substantial progress: more than 3,000 panchayats now have some form of remediation, and the initiative reflects serious political commitment to safe water.

But the authors urge a course correction:

• Representative sampling: Future siting must be guided by robust, statewide water testing, not limited or outdated surveys.

• Transparent criteria: Government agencies should openly share how they classify “affected” areas and decide where to install units.

• Monitoring efficiency: Regular testing of both groundwater and treated water is essential to ensure filters actually work.

• Equity in access: Remote and marginalised communities must be prioritised, even if installation is costlier or logistically tougher.

Without these reforms, the paper warns, Bihar risks continuing a cycle of misallocation: leaving some at risk while others receive interventions they may not need.

Beyond Bihar: a national problem

This story is not Bihar’s alone. Across India, uneven data and fragmented governance make water management a guessing game. Over 14,000 monitoring stations collect groundwater data nationwide, but contamination from arsenic, uranium, and fluoride continues to spread.

Clean water isn’t just a question of installing filters, it’s about planning, coordination, and accountability.

The last glass

Bihar’s groundwater crisis offers a larger lesson: technology alone can’t clean what poor data and uneven governance make dirty. Every misplaced filter is a reminder that evidence, not convenience, must guide public policy.

If Bihar can update its maps, monitor its wells, and plan with fairness, it can turn this failure into a success story for all of India. Until then, millions will continue to draw water from wells that promise life but deliver danger, a stark warning that the map of clean water is not yet drawn right.