That quote is in reference to planet earth and water, if I’m not mistaken.
it's his email to me. and it refers to earth, yes.
but his point, and the thesis that is accepted among the scientific community, is that the presence of water would not need to be on earth or an earth like planet. the physical laws of the universe are just that. there is no difference in physics, chemistry, etc. based on where in the observable universe you are standing. electrons have the same spin, lithium, the same atomic number, photons the same speed through space.
the same applies to biology, although the verification is a lot harder, obviously, but the modeling is the same. (note this doesn't mean there is not some other foundational construct for life. life forms based on certain types of methane, for example, has been theorized).
nevertheless, anyone in the scientific community will tell you that it's an axiom: find water. on earth, mars, or in galaxy GN-z-11 (the most distant in the universe), .... and you'll find some life form.