Biggest swimming pool in the world is located at The hotel San Alfonso del Mar in Chil. It covers  more than 20 acres and clear water transparent to a depth of 35 meters and holds 66 million gallons of water. Building tooks 5 yers and cost nearly USD 2 billion and the annual maintenance is USD 4 million.
What is most interesting to me about this pool, is that hes just few steps from the ocean 🙂

More about big pools: