"But, ironically, the Moon is probably parched and that's why I think GB is wrong. "

The Moon is parched.
The driest deserts on earth have more water than the Moon. But the same could said about Mars which has at least 10 times more water than compared to the Moon.
Mercury also is parched, but it could have water ice at it's poles.

Some NEOs are thought to have 25% of their mass as water.
Suppose a rock 200 meters in diameter had 25% of it's volume as water.
A sphere 200 meters in diameter has about 4 million cubic meters- so if 25% of it's volume is water then it has about 1 million tonnes of water.

We have nearly counted 1000 NEOs which are around 1000 meters or larger. Those NEO which are around 200 meters probably number somewhere around 10,000.

So, one could easily have more than 2 billion tonnes of water in all the NEOs. And the asteroid belt easily has more water than on Earth. But one thing to keep in mind is that in terms millions to billions of years, the NEOs have a temporary existence- they going to be thrown out or hit something.

In terms of mining water in space, you *require* about 1/10th of million tonnes or less. "Quality" is more important than "quantity". 100,000 tonnes of water is 100 million kgs of water, which if sold at average price $200 per kg has a gross worth of 20 billion dollars.

And of the 100,000 tonnes, one might expect that the gross worth of the first 1000 to 10,000 tonnes is about $500 per lb [$1100 per kg].
So one could say, that the first 10 million kgs of the total minable of 100,000 tonnes would determine the viability and the remaining 90,000 tonnes would determine potential growth for investing capital in such an enterprise.
So, one could have situation where there is rich area of water which is within an area of less than 10 sq kilometer inside a crater of 50,000 sq kilometers. This "rich area" of water could have 10 million kg of minable water which could mined within time period of a decade, and the crater could have 90 million kg of less rich areas of water- obviously one would try to start in the best area.
So, 10 million kg of water is 10,000 cubic meters of water- more than in swimming pool, less than in a lake.

If an average of 1 percent per volume of a cubic meter of lunar regolith can extracted from the first meter depth of the 10 sq kilometer area, that is an average of 10 kg of water per sq meter at a meter depth.
1 sq km has 1 million sq meters, so in the first 1 meter of this 10 sq kilometers is 100 million kgs of water- and you need to get 1/10th of this.

On Earth having soil which less than 5% per volume of water is not enough to allow plants to grow. On Earth if a rain gauge indicates that it has rained 1 cm, then over an area of 10 sq kilometers, it has rained about 100 million kgs of water, one needs a rainfall amount equal to 1 mm.
When a desert on earth receives less than 1" of rainfall per year, it is receiving less than 25 mm per year.

So, google: driest region on earth :

"The scientists have come to the Atacama to investigate how much water life needs to survive. Water is necessary for life, but water is so scarce in the Atacama that it is a wonder anything can live there at all. Some parts of the desert have not seen rain for centuries. The desert itself is thought to be between 10 to 15 million years old, making it the oldest desert on Earth.
...
"When is dry too dry for life?" asks Chris McKay, a planetary scientist with NASA Ames. "In the Atacama, we think we have crossed that threshold."

The Atacama, however, is not as dry as Mars. It is not as cold as Mars, either, although it is cooler than most other deserts on Earth. The Atacama enjoys a temperate, Mediterranean-like climate with temperatures ranging between 0 and 23 degrees C (32 to 73 F)."
http://www.astrobio.net/news/article337.html

Mars is wet compared to the Moon. And Atacama is a swamp compared to the Moon.

The other driest place on Earth is:
"in Antarctica in an area called the Dry Valleys, which have seen no rain for nearly 2 million years. There is absolutely no precipitation in this region and it makes up a 4800 square kilometer region of almost no water, ice or snow. Water features include Lake Vida, Lake Vanda, Lake Bonney and the Onyx River."
http://www.universetoday.com/guide-to-space/earth/driest-place-on-earth/

[btw:
"Lake Vanda is a lake in Wright Valley, Victoria Land, Ross Dependency, Antarctica. The lake is 5 km long and has a maximum depth of 69 m. On its shore, New Zealand maintained Vanda Station from 1968 to 1995. Lake Vanda is a hypersaline lake with a salinity more than ten times that of seawater, more than the salinity of the Dead Sea, and perhaps even more than of Lake Assal (Djibouti), which is the world's most saline lake outside of Antarctica."
http://en.wikipedia.org/wiki/Lake_Vanda
If this lake had average depth of 40 m and say 5 km by 2 km- that is about 400 million tonnes of water]

Again, that is wetter than than Mars, and it's a swamp or rainforest compared to the Moon.

Of course the Moon is parched, if you dumped a billion tonnes of water on the the Moon it would still be parched, and it would still be far drier than Mars.

Or a different way of looking at this, is 1 billion tonnes, or 1 trillion kg of water is valued at $100 per kg, it is more money than currently exists on this planet- not that governments are unable to print more.