How to keep water cold?

[PixelStix]

I'm currently using frozen water bottles and switching them regularly to keep it cold, but does anybody know an easier method? My little guy seems a little stressed due to the heat :/

 

[Syn]

If you set up a fan to blow across the surface of the water, it speeds up evaporation and heat transfer, which can drop the water temperature by a few degrees. That's the cheapest, immediate fix aside from using the ice bottles.