Some 347 million children in South Asia suffer from water shortages, according to a report published on Monday by the UN children's aid organization UNICEF.
More than a quarter of all children live in the region, the world's most populous.
According to UNICEF's report, 55% of children in South Asia are affected by a lack of water - the highest rate worldwide.
"Safe water is a basic human right, yet millions of children in South Asia don't have enough to drink in a region plagued by floods, droughts and other extreme weather events, triggered increasingly by climate change," said Sanjay Wijesekera, the UNICEF director responsible for the region.
Ahead of the COP28 UN Climate Change Conference in Dubai at the end of the month, UNICEF is calling on the international community to take steps to ensure a planet worth living on for children.
The report says that the 594 million children globally still lack basic drinking water, sanitation and hygiene services, making them particularly vulnerable to water scarcity and climate-exacerbated hazards, shocks and stresses.
Water scarcity affects the well-being and growth of children, creates food insecurity, malnutrition and diarrhoeal diseases.
Water scarcity also affects agriculture, industry and economic growth. And if farming families are doing badly, children are more likely to be forced into child labour, the report said.
Last year across South Asia, 45 million children lacked access to basic drinking water supplies - more than any other region. But UNICEF said services were expanding rapidly, and hoped that number would be halved by 2030.