UNITED NATION (AP) — The United Nations chief urged the first world conference on water in over 45 years on Wednesday, to address the "21st century emergency" that is wasting the world's most important resource and has left billions of people without clean water and basic sanitation.

Secretary General Antonio Guterres told the opening session that water is "humanity's lifeblood" and a human right, but the world is draining it "through vampiric overconsumption and unsustainable use and evaporating it through global heating".

In a challenge to all nations and the broader international community, he said the three-day conference must represent "a quantum leap" in recognition of the vital importance of water and the need for action to ensure its sustainable use.

Guterres called for "game-changing commitments" toward UN goals, including ensuring that all people have access to drinking water and sanitation by 2030.

The UN secretary general called for major investments in water and sanitation systems and efforts to address climate change, stressing that "climate action and a sustainable water future are two sides of the same coin".

According to conference organisers, such commitments will be the key outcome of the conference. Already, more than 500 commitments have been registered from governments, UN agencies, business leaders and civil society, they say.

Just before the conference opened, US Ambassador Linda Thomas-Greenfield announced a new commitment from the Biden Administration of US$49 billion to be put toward "equitable, climate-resilient water and sanitation investments at home and around the world".

She said the new US funding "will help create jobs, prevent conflicts, safeguard public health, reduce the risk of famine and hunger, and enable us to respond to climate change and natural disasters".

But the US envoy stressed the need for global cooperation and urged the UN Security Council to take up the issue of water scarcity, which exacerbates conflicts and disrupts peace and security.