i objected to the duolingo gods with this one... 'una alberca' also means 'a pool', according to the earlier versions of this website....
Welll...as much as I would like to protest, alberca looks like it strictly means "swimming pool". So the next time you see a puddle of water and want to say "There is a pool of water." Say "Hay una piscina de agua" or else your children will rip off their clothes and jump in the "alberca" (swimming pool).
A Puddle of water = Un charco de agua. A Piscina is just another way to say Alberca, but of course deppending on the country there could be some differeces in meaning. «Puddle of water» is not one of them though.