Our Solar System alone has megatons of water in the form of ice in
billions of comets which will be far easier to access than landing and
taking off from Earth. Most of the outer planet moons are made of
ice as well and some of them like Europa have lots of liquid water. In
fact Europa has twice the amount of water than in all of Earth's oceans.

Even more important, we already know other solar systems have their
own comet belts, so it is safe to assume that many systems have their
own supplies of naturally frozen water. So the ETI don't even need to
travel here or very far if they are that thirsty.

I have never bought into the idea that our planet is so rare and
precious that everybody else in the galaxy wants it for themselves.

As for “saving” us, are ETI that altruistic that their benevolence
extends to truly alien beings? And how do they know that their idea
of saving us is what we want or need? Anyone saying they were here
to “rescue” us would have me immediately asking what they want in
return. No one would come this far just to be nice to us.

Look at our current attitude towards the galaxy. The general
consensus I see is that we want to know if there are Earthlike worlds
not to see if anyone lives on them that might need our help, but with
the hope that we might want to live there ourselves someday. The
possibility that these planets may already be occupied is no minor issue
if we want to colonize the Milky Way with human beings and require
planets like the one we have now.

Of course I don’t think the descendants from this planet who will
occupy the galaxy one day will require Earthlike planets to survive, but
that is another matter for now. There is the distinct possibility that the
first people who leave our Solar System for the stars will still be
baseline humans looking for a new place to live away from mainstream
human society, which may be repressing them for political or religious
reasons, or both. Or they will be people who just want a new start
away from Earth and its immediate celestial neighbors.

Since we will likely know a number of Earth-type exoworlds by then,
what if they decide to head there to colonize? What will they do with
any inhabitants already there? Does anyone think they will attempt
to “save” them, or are we talking another Native American situation again - unless the natives are pretty advanced themselves?

Maybe I am just too primitive to think past a predator-prey situation,
but we really need to ask ourselves why would an ETI come here?
If they are just exploring, why have a whole crew of beings aboard?
Wouldn't an automated probe do just as nicely? And if they are only
studying us, wouldn't they be trying not to make themselves known
to us in any way?

It is too much of a copout to simply say that we can't conceive what
an alien mind might think or do. If they do ever come here, they will
have some kind of motive and it may not necessarily be for our benefit.
It may be nothing personal, either, but that doesn't mean we will be
any safer for it.

We are already looking for other Earths with the intent to colonize
them and we haven't even got a decent star drive yet, so why should
we assume that an ETI won't be thinking any differently?

Maybe that's what the crop circles are: Landing markers for the colonists.