The world could suffer a 40 percent shortfall in water in just 15 years unless countries dramatically change their use of the resource, a United Nations report warned Friday.

Many underground water reserves are already running low, while rainfall patterns are predicted to become more erratic with climate change. As the world's population grows to an expected 9 billion by 2050, more groundwater will be needed for farming, industry and personal consumption.

With "business as usual" the world is facing a "collapse in our global socioeconomic system," Richard Connor, lead author of the report, told Reuters.

The report predicts global water demand will increase 55 percent by 2050, while reserves dwindle. If current usage trends don't change, the world will have only 60 percent of the water it needs in 2030, it said.

Having less available water risks catastrophe on many fronts: crops could fail, ecosystems could break down, industries could collapse, disease and poverty could worsen, and violent conflicts over access to water could become more frequent.

"Unless the balance between demand and finite supplies is restored, the world will face an increasingly severe global water deficit," the annual World Water Development Report said, noting that more efficient use could guarantee enough supply in the future.

By 2050 two thirds of the world's population will be living in cities, and demand for water is expected to grow related to urbanization in developing countries. Urbanization means that access to safe water and adequate sanitation, although typically higher in cities, has decreased in the fastest growing urban areas.

One example is sub-Saharan Africa, where urbanization — often unplanned — is happening most rapidly. Here the proportion of people who have piped water on their premises has fallen to 34 percent from 42 percent since 1990.

"The spontaneous urbanization, which creates slums, makes it very difficult because of the layout of the slums to provide water," Joan Clos, executive director of the United Nations Human Settlements Program (UN-HABITAT), told Reuters.

The report, released in New Delhi two days before World Water Day, calls on policymakers and communities to rethink water policies, urging more conservation as well as recycling of wastewater as is done in Singapore. Countries may also want to consider raising prices for water, as well as searching for ways to make water-intensive sectors more efficient and less polluting, it said.

In many countries including India, water use is largely unregulated and often wasteful. Pollution of water is often ignored and unpunished. At least 80 percent of India's population relies on groundwater for drinking to avoid bacteria-infested surface waters.

In agriculture-intense India, where studies show some aquifers are being depleted at the world's fastest rates, the shortfall has been forecast at 50 percent or even higher. Climate change is expected to make the situation worse, as higher temperatures and more erratic weather patterns could disrupt rainfall.

Currently, about 748 million people worldwide have poor access to clean drinking water, the report said, cautioning that economic growth alone is not the solution — and could make the situation worse unless reforms ensure more efficiency and less pollution.

"Unsustainable development pathways and governance failures have affected the quality and availability of water resources, compromising their capacity to generate social and economic benefits," it said. "Economic growth itself is not a guarantee for wider social progress."

Wire services