Largest Pool in the World, Chile.

World's largest pool which holds 66m gallons is so big you can even sail boats on it.

 San Alfonso del Mar is a private resort in Algarrobo, Chile, about 100 km (62 mi) west of Santiago.The resort has the world's largest swimming pool 

 The pool was developed by Fernando Fischmann;  his Chilean company Crystal Lagoons built the pool, which opened in  December 2006. Early estimates put the total cost of construction at  about US$3.5 million for the filtration system alone.

The pool is 1,013 m (3,323 ft) long, covering 8 ha (20 acres), containing some 250 million liters (66 million US gallons)of seawater, with a maximum depth of 11.5 ft (3.5052 m). The water is pumped from the Pacific Ocean, filtered, and treated. 

(Source Wikipedia)