Reaction is……2 H2O <_-_-_-_-_-> OH^- + H3O ^+
In autoprolysis………we take two identical molecules……as u asked for water so…….we will take two identical water molecule but remember……one of them will act as” Brønsted acid” and other will act as “Brønsted base”……Brønsted was a scientist who gave a theory and the theory was..that…….” when acid and base will react then acid will form its conjugated base and base will form its conjugated acid”…….so…..when 2 water molecules will react with each other in this condition then Brønsted acid will release a proton and Brønsted base will accept it…….