Which nonprofits wield the most influence on Twitter?

It’s not one of America’s most established or best-known organizations. It’s Charity: Water, a new global-development group that has 1.3 million followers, far more than any other charitable group we could find.

To come up with a list of the top groups on Twitter, based on their number of followers, we only considered an organization’s official Twitter page. We did not add up followers for organizations with multiple pages (United Way Worldwide, for example, has dozens of local organizations), and we did not include well-known personal accounts associated with an organization. (Otherwise, Doug Ulman, president of Livestrong, the charity founded by the cyclist Lance Armstrong, would have been near the top with his more than 990,000 followers.)

Following are the counts for the top charities, based on how many followers they had as of the middle of this week.

1. Charity: Water (@charitywater) 1,308,128
2. Room to Read (@RoomtoRead) 457,158
3. ONE (@ONECampaign) 452,002
4. The Bill & Melinda Gates Foundation (@gatesfoundation) 430,549
5. DoSomething.org (@dosomething) 366,737
6. Water.org (@Water) 365,230
7. Creative Commons (@creativecommons) 364,809
8. Kiva (@Kiva) 357,148
9. Care (@CARE) 350,785
10. The Case Foundation (@CaseFoundation) 338,283
11. Acumen Fund (@acumenfund) 326,138
12. Ashoka (@AshokaTweets) 322,734
13. Skoll Foundation (@SkollFoundation) 320,057
14. Samasource (@Samasource) 314,298
15. Witness (@witnessorg) 276,553
16. Unicef (@UNICEF) 209,690
17. American Red Cross (@RedCross) 208,660
18. World Wildlife Fund (@WWF) 159,353
19. Greenpeace International (@Greenpeace) 109,579
20. Save the Children (@savethechildren) 106,162