Water on the Moon

Heard on the radio today:

Host: Water on the moon . . . water on the moon . . . what are we supposed to think about this? And why should we care?

Caller: Well, finding water in a permanently shadowed lunar crater is actually very significant. The presence of water on the moon could help sustain lunar colonization. Water is a necessity, and it's very, very heavy, so transporting it up there is not a good option. If, however, there's water on the moon . . .

Host: Well, now, wait a minute. Water's not the only necessity. Let's say we've colonized the moon, and your local Lunar Costco, or your Tranquility Base Wal-Mart, runs out of Triscuits--

Caller: Well, you're not going to necessarily have a Wal-Mart on the moon.

Host: Well, if there are people there, don't you need a neighborhood grocery store?

Caller: Ah, maybe not. But if you have significant amounts of water there, you can plant and grow crops to help sustain life.

Host: You sound like you know what you're talking about. What do you do for a living?

Caller: I'm an aerospace engineer.

Host: Ah! A rocket scientist.