Depending on where you live, the water could still be cold during summer. If you live by a mountain a river coming from it could be cold enough to chill your brew, even during august.
A deep lake can be very cold at the bottom. If you really need to keep something cold, you could lower it to the bottom, and keep it there for long periods of time. It would just take some extra time to retrieve it.
"Hey, surprise guests! Just give me an hour, and I'll get you folks some chilled pate from my lake-storage"
If you have sun, you can also utilize
evaporation to cool a container.