the implication is that they have a lot of water but it's unpalatable or toxic most of the time and needs filtering I think - easy matches but most of them bad?

Most men are insane from frustration, not unpalatable or toxic.

If the first part of your description is true, then the second needs corrected by replacing the "not...or..." with "therefore...and...".

"Insane from frustration" explains, rather than contradicts, "unpalatable" and "toxic".

People generally do not want to have an insane, frustrated partner.

It's literally enough to sip the surrounding water, it's that easy. Truly toxic frustrated people never have problem with finding sexual partners.

The one I heard was "dying of thirst in the swamp." Lots and lots of water, but nothing you can stomach.