Were you to run it thru a water chiller (aquarium supply shop) or an aluminum radiator of some sort, I could see that may work. But keeping warm water in an aluminum box, you'll have a aluminum box of warm water.

Something that comes up often in the Reef Tank Forums is "what about 'coiling' the supply hose thru a fridge...?"
Well, running it thru a fridge (a very popular subject in the Reef Tank Forums where temperature is life and death for an entire eco-system) will kill a fridge. A fridge motor is designed to come on every once in a while, for very short periods in order to maintain a constant temp. Running a hose thru it in an attempt to cool the water overworks the motor, killing the fridge in a matter of days or weeks. (The heat emanating from the hose tells the fridge to keep running)

For my purposes, I wouldn't get the water tube thingy without at least a 1/10 hp water cooler. 1/10 HP (Mini) Current USA Prime Inline Chiller
The one above is a top-end model, but you'll still pay a hefty price regardless.
Used Equipment forums on the Marine Aquarium or Coral websites, is a good place to find loads of stuff for ones grow...especially if our sponsors don't carry it at present. Perhaps more trustworthy than ebay, too. (Freshwater equipment is lower quality, and may not withstand nutes and additives) :thumbsup:

Jeepers...only 9:45 and I think I've had my fill of coffee, lol.