My high-school chemistry teacher claimed that hot water is inferior at storing dissolved gasses, and that hot water has probably been sitting in the plumbing system for some time, so a great deal of the dissolved oxygen gas has been expelled. On the other hand, cold water from the taps is more "fresh" and enriched with oxygen gas. Even after boiling water, the trapped gases will take some time before they escape. So if you start with cold water, whatever you're cooking with the water will become more enriched with oxygen gas than if you started with warm water.

Dissolved oxygen gas = tasty?