Earth might have a subsurface ocean as well [1], though I haven't found any follow up since 2014 on that one.

[1] http://dx.doi.org/10.1126/science.1253358

>They conclude that the mantle transition zone--410 to 660 km below the Earth's surface--acts as a large reservoir of water.

Sadly there will be no eyeless space whales in our basement, given that the temperature at that depth on Earth is around 2,000° Celsius.

I like this line of thinking way better lol

That sounds like water in hydrated minerals rather than liquid water? In terms of settling inner solar system asteroids where the sun bakes everything you're looking for material with as much easily extractable water as concrete to make a comfortable home.

> whales across the universe

and bowls of petunias

Oh no, not again!