There's a known form of it, called tritiated water, which has tritium atoms instead of hydrogen. This water is radioactive, and occurs naturally. However, it doesn't last forever due to the usual radioactive decay and has low energy.
This water emits a beta particle, of a theoretically non hazard nature. It stays in the body less than fifteen days.
Although with the recent disaster of Fukishima, the media was talking about more than tritiated water. In fact, water with high levels of radioactivity could create a serious risk toward near locations and population.
When radioactive water hit oceans, rivers or other systems that carry it, the event could be a disaster of great proportions. Maybe the worst of all, is that continues looking inoffensive like any other.
Nuclear energy shouldn't be utilized inside the planet!