dahka's population, now estimated at 15 million, is expected to hit 20 million by 2025. >> dahka is one of the mega cities which is growing too too fast. >> reporter: country director for the charity water aid, says the increased pop laying density is severely taxing the city's ability to house and care for its people. >> almost 5,000 slums are in and around dahka city. almost one third of the population are living in... at the low-income communities. most of them don't have ownership over those pieces of land. but the main challenge is provisioning essential services for this huge number of population, mainly water and sanitation. >> reporter: with 2,000 newcomers daily, the struggle to find clean water in the slums often hasife-threatening consequences. >> water? yes, we have water but the water is not always available. when water is available, it is often bad. yesterday a woman here thought she had cholera. she went to the hospital, but she died last night. >> reporter: if you wan to see the human toll exacted by unsafe water and poor sanitation in dahka, you come here. this is the o