I realise this is nothing new, just a simple tip for some who mightn't be aware.
I should emphasise that I would only use this system of water cooling on warm summer nights. When ambient temperature gets below 18 or so degrees I don't generally need water. On the relatively mild winter nights in Newcastle the STL TEC gets further than minus 20 without water, but I still think minus 20 will be good enough to get the noise down.
This site has some quite detailed info on water chilling (plus some interesting theory on autoguiding)
http://aajonahfish.com/watercooling.htm
Running the water through a gamer's CPU water radiator/cooler is another 'passive' option. You'll also find that some aquarium coolers are expensive - usually the ones designed for saltwater.