Homosapiens: Yes, cold water does prolong the life of the worms too. But I have long ruled out the option as I don't fancy an open tray of worms in my fridge.
Superlamon: Ketapang is antibacterial and antifungal. This could be the reason. I've heard of hobbyists using antibiotics to keep the tubifex worms water from fouling up. But there are dangers involved in using antibiotics apart from the danger to the pocket.
Johannes: I used tap water treated with the blackwater++ that my wife prepared. But I suspect that ketapang water will do the same trick.
/John