Started by Samuel Gurney MP and the barrister, Edward Thomas Wakefield. Founded as the Metropolitan Free Drinking Fountain Association it changed its name to include cattle troughs in 1867. London Details have a terrific post about this organisation.
MDFCTA is a great site, aiming to collect all these troughs and fountains, and not just those in London. Do let them know of any they don't yet have.
Now the Drinking Fountain Association, they are still trying to provide water to the public - probably more difficult now than when they started.