D₂O, and then make a living selling my piss to chemical manufacturers
e:
How Drinking Heavy Water Could Kill You
Algae and bacteria can live with 100% heavy water and no regular water. Plant and animal cells are more complex, so too much heavy water results in sickness or death. One key issue is that heavy water disrupts mitosis, the type of cell division used to repair injuries and grow new cells. The mitotic spindles of cells containing too much heavy water simply aren’t able to equally divide a cell to form two identical new ones.
But, you have to continuously drink and eat only heavy water for several days to see an effect. Replacing 20% of regular water in cells with heavy water is survivable for humans and other mammals (although not recommended). Swapping 25% of water with heavy water causes (sometimes irreversible) sterilization. Replacing 50% of water with heavy water is lethal. It’s not a pretty death, either. Heavy water poisoning resembles radiation poisoning or cytotoxic poisoning from chemotherapy.
It's pretty impressive how much we can tolerate, honestly. I remember they were accidentally using it in a water cooler at a nuclear power plant for a while, and everybody was fine.