Fiji's Prime Minister Frank Bainimarama says the lack of clean water will be responsible for health problems and conflicts around the world.
Mr Bainimarama warns the world's climate is heading towards at least a three-degree warming, and global reductions in crop yields will bring malnutrition, disease and death.
He called on the world's major economies to live up to their commitment of meeting the 1.5-degree target and boost public and private financing to 100 billion US dollars a year by 2020.
"As water resources dry out, we're going to see massive waves of migration out of what will become inhospitable regions in the world. Countries that share common water supplies will see their diplomatic relations tested. Conflicts will emerge."
"Not over ideological differences. But over the most basic resources such as water, and other fundamental building blocks for human development," Mr Bainimarama said.
Frank Bainimarama was at the UN meeting on interlinkages between water and climate action in New York this week.
Mr Bainimarama said if current trends continued, climate-induced water stress would become more prevalent.
He said rising sea levels and stronger cyclones would create more intense storm surges, washing salt water into freshwater aquifers; destroying vital water sources in island and coastal communities.
"But the devastation won't be limited to the coasts. The rainy seasons will bring even more intense floods, drowning entire communities, while the dry seasons will bring even longer droughts, scorching farmlands, destroying crops, and parching vast numbers of people by depleting ground water resources."
"For Fiji, when it comes to accessing clean water, half a degree difference in global temperature can mean the very difference between life and death for millions of people," he said.
Mr Bainimarama said the goal of the Paris Agreement was to hold the increase in the global average temperature to well below 2 degrees Celsius above pre-industrial levels and pursue efforts to limit the temperature increase to 1.5 degrees Celsius.
"Following the release of IPCC's report last year, we now know just how much that half a degree matters."
"When the leaders of the world gather here at the UN Secretary General's Climate Summit later this year, we have an important opportunity to change this future - to chart a new course - to join Fiji and the Marshall Islands in their commitment to enhance their NDCs and develop long-term strategies."
"If we can do it, so can you."