NASA Administrator Jim Bridenstine has a vision for renewed and "sustainable" human exploration of the moon, and he cites the existence of water on the lunar surface as a key to chances for success.

"We know that there's hundreds of billions of tons of water ice on the surface of the moon," Bridenstine said in a Reuters TV interview in Washington on Tuesday, a day after NASA unveiled its analysis of data collected from lunar orbit by a spacecraft from India.

The findings, published on Monday, mark the first time scientists have confirmed by direct observation the presence of water on the moon's surface - in hundreds of patches of ice deposited in the darkest and coldest reaches of its polar regions.

The discovery holds tantalizing implications for efforts to return humans to the moon for the first time in half a century. The presence of water offers a potentially valuable resource not only for drinking but for producing more rocket fuel and oxygen to breathe.

Bridenstine, a former US Navy fighter pilot and Oklahoma congressman tapped by President Donald Trump in April as NASA chief, spoke about "hundreds of billions of tons" of water ice that he said were now known to be available on the lunar surface.

But much remains to be learned.

NASA lunar scientist Sarah Noble told Reuters separately by phone that it is still unknown how much ice is actually present on the moon and how easy it would be to extract in sufficient quantities to be of practical use.

"We have lots of models that give us different answers. We can't know how much water there is," she said, adding that it will ultimately take surface exploration by robotic landers or rovers, in more than one place, to find out.

Most of the newly confirmed frozen water is concentrated in the shadows of craters at both poles, where the temperature never rises higher than minus-250 degrees Fahrenheit.