Water As Shielding

I don't want to build it out of sapphire for the sake of glitz or
bling, I want to build it out of sapphire because of sapphire's
wonderful properties and because of the fact that aluminum and oxygen
are fairly common. For instance, it has been suggested to build a
Stanford Torus out of one million tons of aluminum derived from lunar
regolith. Well, the regolith contains more oxygen than it does
aluminum, so if you could use both, you wouldn't have to mine as much,
which would save money. And that's even assuming you wanted to use a
million tons. If sapphire is so strong, tough, etc., you might want
to use 750,000 Kg or even 500,000 Kg.