"Every time it rains it washes toxins into the ground water. We have ample evidence going back many years."
Chief Minister of Madhya Pradesh Shivraj Chouhan dismisses the claims.
In an interview with the BBC to mark the 25th anniversary of the disaster, he told me that the communities around the plant had been supplied with clean drinking water.
"It took some time," he said. "But... we can say that we are providing 100% clean water."
The Union Carbide plant had also been made safe, he said.
Campaigners angrily dismissed his claims.
"Even with people who settled here long after the gas," says Satinath Sarangi, "what we find is a very high incidence of diseases: damage to the kidneys, the liver, the brain, the skin. The incidence of birth defects in these areas is at least 10 times what you would find in similar socio-economic populations."
In a neighbourhood just north of the Union Carbide plant, we found people drawing groundwater from a pump. We took a sample and had it tested at a laboratory in the United Kingdom.
The test found that it contained nearly 4,000 micrograms per litre of carbon tetrachloride - nearly 1,000 times the World Health Organisation's safe limit. "Carbon tet", as it is known, is a highly toxic pollutant which is known to cause cancer and liver damage.
In 1989, Union Carbide reached an out-of-court settlement with the government of India.
The company agreed to pay $470 million. The Indian government had initially demanded nearly 10 times that.
The money built a hospital for those who continued to suffer ill-health. The survivors of the gas got about $1,000 each in compensation.
The agreement represented a full and final settlement of Union Carbide's civil and criminal liabilities.
'Night of the gas'
"The environmental damage caused by the toxic contamination was never part of that settlement," says Mr Sarangi.
The night of the gas leak continues to haunt the people of Bhopal
"Very little was known about the toxic contamination at the time. Data started coming out in 1990 and 1991 about the high levels of organochlorines, talids, polynuclear aromatic hydrocarbons and heavy metals."
Sambhavna, the charity Mr Sarangi runs, wants Dow Chemical, the US company that bought Union Carbide, to pay to clean up the ground.
In a statement the company said: "The groundwater issue at the Bhopal site is best addressed by the state government of Madhya Pradesh, which owns the site and is responsible for clean-up activities.
"Our understanding is that the central and state governments have plans for the site clean-up and we're hopeful they will follow through with their remediation plans, including addressing concerns about groundwater."
For Union Carbide the matter is, in a legal sense, closed.
For the people of the affected areas, it is far from closed.
In 25 years, no-one has been successfully prosecuted, either for the original leak, or for the continuing alleged groundwater contamination.
And the shadow of what happened on that toxic night reaches down through the decades, and into the lives of generations who were not even born on what everyone in Bhopal refers to as "the night of the gas".
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