BRASILIA: Water rationing in Brazil's capital - one of an increasing number of cities facing shortages - will end by December with the completion of an expanded supply system, said the region's governor.

Water is under pressure globally as the planet warms and demand grows along with populations, according to a United Nations report launched this week at the World Water Forum in the South American nation's capital, Brasilia.

"Water has become a global problem," said Federal District Governor Rodrigo Rollemberg during a panel discussion on Tuesday at the forum, the world's largest water-related event.

"Here in Brasilia it is no different."

The water supply has declined due to low rainfall as well as rapid and disorderly growth in Brasilia, which is part of the Federal District, Rollemberg said.

In January 2016, after three years of rain scarcity, district authorities enforced water rationing.

The governments of the Federal District and Goias State, which surrounds it, also invested a combined $166 million to develop water infrastructure.

When construction finishes by December, the expanded system will provide 2,800 liters of water per second to the Federal District's 3 million people, and the same amount to Goias, said Rollemberg.

About 16 percent of Brazil's 5,570 cities face water issues, according to data from the Ministry of National Integration.

Globally, demand is expected to increase by nearly one-third by 2050, when 5 billion people could be left with poor access to water, the UN warned in its 2018 World Water Development Report.

To avoid such a crisis, the UN recommended "nature-based solutions" that use or mimic natural processes to increase water availability.

Those include changing farming practices so the soil retains more moisture and nutrients, harvesting rainwater, conserving wetlands that capture runoff and decontaminate water, restoring floodplains, and turning rooftops into gardens.

Such initiatives will become more important as water-intensive industries grow.

By 2025, the global demand for agriculture is expected to rise by about 60 percent, and energy production by around 80 percent, the report said.