Received email regarding the subject. Quite concerned as I also use that thermal pot which boils water and keeps the water warm. The message, also published by sinchew daily, says it is harmful to keep reboiling water, according to Singaporean pharmacist:-
A forumer refutes it, "Water is H2O. Boiling it will not change its chemical composition. Neither will reboiling it.", he said. Read more HERE.
Another says, "Water is H20. Hot water is still H20. There's no way to get a nitrate out of it.". Read more HERE.