"India irrigates its deserts and dumps extra water on Pakistan without any warning," the bearded Saeed told Reuters, as he surveyed a vast expanse of muddy water from a rescue boat just outside the central city of Multan.
"If we don't stop India now, Pakistan will continue to face this danger."
His comments will surprise few in India, where Saeed is suspected of helping mastermind the 2008 Mumbai massacre which killed 166 people, a few of them Americans. Saeed, who also has a $10 million US bounty on his head, denies involvement.
But his presence in the flood-hit area is part of a push by Pakistani Islamists, militants and organisations linked to them to fill the vacuum left by struggling local authorities and turn people against a neighbour long viewed with deep mistrust.
Water is an emotive issue in Pakistan, whose rapidly rising population depends on snow-fed Himalayan rivers for everything from drinking water to agriculture.
Many Pakistanis believe that rival India uses its upstream dams to manipulate how much water flows down to Pakistani wheat and cotton fields, with some describing it as a "water bomb" designed to weaken its neighbour.
There is no evidence to prove that, and India has long dismissed such accusations as nonsense. Experts say this month's floods, which also hit India's part of the disputed Kashmir region, were caused by the sheer volume of rainfall.
In fact, some Pakistanis accuse their own government of failing to invest in dams and other infrastructure needed to regulate water levels through wet and dry seasons.
But others agree with the narrative pushed by Saeed and Syed Salahuddin, head of the militant anti-Indian Hizbul Mujahideen group and also one of India's most wanted men.
"India wants to turn Pakistan into an arid desert," Salahuddin told Reuters in a telephone interview, describing another scenario feared by some Pakistanis - that India will cut off supplies of water in times of shortage.
"If this continues, a new Jihad will begin. Our fighters and all of Pakistan's fighters are ready to avenge Indian brutality in whatever form."
Saeed's charity, Jamaat-ud-Dawa (JuD), has sent hundreds of workers to areas of Pakistan worst affected by the floods, where they distribute food and medicine at the same time as spreading the organisation's hardline ideology against India.
JuD is believed by many experts to be a front for Lashkar-e-Taiba, the militant group which India says carried out the Mumbai attack. Saeed was a co-founder of Lashkar-e-Taiba, but he has played down his links to the group in recent years.
"This is a premeditated plan by India to make Pakistan suffer," Abdur Rauf, who has worked as a JuD volunteer for 16 years, told Reuters, as he prepared to distribute medicine and syringes at a relief camp near Multan.
"Don't be fooled. This water bomb is no different from the atom bomb. It's worse."
Officials in India's water resources ministry this week declined to respond to charges of "water terrorism", saying they were being stoked by militants, not the Pakistani government.
Much of the Indian-held side of Kashmir has also been hit by flooding, the worst in that region for more than a century, and officials have put the death toll there at more than 200.
"This is not a mistake: this is a deliberate act to destroy Pakistan and make its people suffer," said Syed Ali, a farmer, as he looked forlornly at the murky waters covering his village of Sher Shah in central Pakistan.
Disagreement over how to share the waters of the Indus river, which flows from India into Pakistan, has dogged the nuclear-armed rivals since independence in 1947.
The neighbours have fought two of their three wars over the disputed Himalayan territory of Kashmir and observers are worried that the next conflict could be over water.
The lives of more than two million people were affected by this month's floods in Pakistan, and more than 300 were killed.
Some are critical of their own government, saying the mass devastation caused by the latest floods was a result of Pakistan's own inefficiencies.
"Some people will say India released the waters," Yousaf Raza Gillani, a former Pakistani prime minister, told Reuters.
"But my question is: even if there was a timely warning from India that this was about to happen, would we have heeded it? Would this government have taken the right steps? I doubt it."
Husain Haqqani, a former Pakistan ambassador to the United States and now a director at the Hudson Institute in Washington D.C., said that water issues are being exploited to keep relations between the two countries tense.
"The Pakistani militants' claims about floods in Pakistan being the result of India releasing torrents of water are downright absurd," he said.
"It is part of propaganda rooted in the belief that Pakistanis must be made to see India as their permanent enemy. Blaming India also covers up for Pakistan's own failure in water management."
Disputes over water-sharing are a global phenomenon, stoked by rapidly growing populations and increasingly unpredictable climate patterns. In South Asia, home to a fifth of humanity, the problem is particularly acute.
"Regional flooding in South Asia is certainly linked to climate change effects. In recent years there has been major glacial recession on Pakistani mountains, and monsoon rains have been unusually and even unprecedentedly intense," said Michael Kugelman at the Woodrow Wilson International Center.
"At the same time, I’d argue that ... human-made actions are making things even worse. Deforestation in Pakistan, for example, has caused floodwaters to rage even more," he said.
The region's three major rivers - the Indus, the Ganges and the Brahmaputra - sustain both countries' breadbasket states and many of their major cities, including New Delhi and Islamabad.
In Pakistan, agriculture contributes to about a quarter of its gross domestic product, and the country still relies on a network of irrigation canals built by the British.
Hoping to resolve the issue once and for all, the two countries signed the Indus Water Treaty in 1960, but India's ambitious irrigation plans and construction of thousands of upstream dams continued to irk Pakistan.
India says its use of upstream water is strictly in line with the 1960 agreement.
According to a 2012 Indian government report, the country operates 4,846 dams in the region - a huge number compared with just a few dozen on the Pakistani side of the disputed border.
"We can't blame India for our own mistakes," said Malik Abdul Ghaffar Dogar, the ruling party lawmaker from Multan.
"We turn every dam project into a political deadlock and a stick to beat our political opponents with, but the truth is this country needs dams and it's just not building any."