What episode number of the series is "open water"?
CREATE TABLE "table1_27910411_1" (
  "no_in_series" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "u_s_viewers_millions" text
);
SELECT "no_in_series" FROM "table1_27910411_1" WHERE "title"='\"Open Water\"';