I've donated to this organization several times (though not as much as I'd like, being only a grad student). I learned about them from another research group testing their drinking water filter pots. I especially like that they train others to set up self-sustaining filter facilities, instead of simply giving out pots without guidance. I've heard from many sources that working with communities this way is the best way to help!
I've also purchased a product off their website and donated to have a card sent to a friend, and both items were handled well.
Finally, I greatly respect the leadership for taking very little salary and putting most funds toward good works (according to their tax forms). While I don't choose charities based on this, it does show how invested they are in their work.
Review from Guidestar