You need a large volume of water, and it needs to be very cold. If you have 5 gallons of wort at 212 F and 5 gallons of ice water at 32 F and perfect efficiency you would end up with all the liquid halfway in between at 122 F. If you increase the volume of ice water to 20 gallons then you end up at 68 F. If your barrel of water is not freezing cold, then you need a lot more of it. If your water is only 50 F then you need 35-40 gallons to get down below 70 F.
I use sink water until the wort temperature gets down to about 120 F, then I pump from a container of ice water, and when the discharge water drops to around 70 F I recirculate it. Recirculating hot discharge water into your cold source water is inefficient.