Doc,
It wouldn't hurt you to drink it. But it would cost you to do so. Heavy water costs hundreds of dollars per gallon.
The Canadians use heavy water in their nuclear power reactors. It acts as both coolant and moderator(a moderator in a reactor is used to slow down the neutrons and make them available to split atoms, thereby allowing the reaction to continue). The fact that the hydrogen atoms in heavy water already have a neutron in the nucleus, they will not absorb a neutron. Normal or "light" water will, thereby absorbing some neutrons that would be available for fission. This property allows Canadian reactors to use natural, unenriched Uranium for fuel. American reactors use enriched Uranium fuel and normal water for both coolant and moderator.
Enrichment refers to the U235 isotope content. U235 makes up 0. 8% of natural Uranium and is fissile(splittable). This is the nuclear fuel reactors run on. American reactors need this isotope enriched to 3-4% before they can operate with light water acting as a moderator.
This enrichment process is very expensive. American power companies have chosen to use expensive fuel, and cheap coolant. The Canadians have chosen to use cheap fuel and expensive coolant. This is probably much more than any of you wanted to know, but here it is.
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