Can you imagine the logistics of trying to fill a pool that size with fresh water? Where would you get it?
That's not a huge deal. 66 million gallons is a lot, but not an outrageous amount of water to obtain. Assuming $1/1k gallons, that's $66k to fill it. That's probably close to the monthly usage for a medium sized town. In the US, the average person uses about 100 gallons/day, so that's about the monthly use of 22k people.
The real issue is treating and cycling the water, just like your freshwater pool at home. You'd need an absolutely ridiculous amount of chlorine. If it was in the US, I'd imagine there would be crazy ecological pressures around it. Chile might be cool with it, but it's still much easier to use ocean water that they can dump right back in when cycling it.