Six thousand children under the age of five die every day because they are forced to drink dirty water - and this could get worse.
The supply of clean water available for each person could fall by a third over the next 20 years, the UN's warned.
Water supplies are dropping because:
- The population is going up so more people need water
- Pollution is destroying fresh water supplies
- Global warming means there will be less rain
The UN says more must be done to cut pollution and waste.