"The third element" is lithium
POTUS mentioned it 2 times, related to water
Lithium is found naturally in water
Lithium in drinking water and suicide prevention: The largest nationwide epidemiological study from Japan
Conclusions: The present findings reconfirm the inverse association between lithium levels in drinking water and suicide rates particularly in the male population.
https://pubmed.ncbi.nlm.nih.gov/32780508/