Living with the Elderly, Part I: Do Not Reboil Drinking Water - Myth or Fact?

My parents and grandparent are in town for 1 week to visit their beloved daughters and granddaughters (my sisters and I). They will be staying with us for 1 week, and by the 2nd day of staying together, a few interesting issues pop up, which in the opinion of the older generation are time-tested truth, but to me, may be just an old folks myth?

First, is it safe to drink reboiled water? 

This issue emerged one afternoon, when my grandma spotted me adding water to refill the half-full thermo pot after making coffee.

The thermo pot I was caught adding water to

Straight away grandma said:"What are you doing? You shouldn't reboil water for more than once!". 

Then my dad rushed to the kitchen from the living hall to join the forum:"Yes, it's true you know, it's in the newspaper. You really shouldn't reboil water...". 

I said:"But it's a thermo pot, it will automatically reboil water when the temperature drop and keep warm, and reboil and keep warm...by the way, what's the logic for not to reboil water?"

Both grandma and dad said:"Everyone said so. You shouldn't reboil drinking water...it's harmful to your health. Whatever the reason, it's for your own safety. So empty the pot first before add new water."

The next day, whenever I stand near the thermo pot, grandma will try to remind me again, and again, and again that it's harmful to use reboil water...So this gives me enough motivation to do a small research online for some information on whether it's really harmful to reboil drinking water, and the scientific explanation of it if it's true.

Like what dad said, there was a newspaper reporting about the harmful effects of drinking reboiled water. 

Harmful to reboil drinking water?

Source and date of the newspaper - unclear. 

How true is the claim in the newspaper article - unclear. 

Have the newspaper editor studied and checked the reliability of the source of their articles before publication - unclear.

Is it a mere marketing gimmick by some water filter company - unclear.

I couldn't find any supporting journals or researches that echo the claim by this chemist from Singapore, who reports that reboiling drinking will transform the harmless nitrates to the nitrites, which is harmful to human body. 

But there is an article from http://nutrition.about.com/ that says:"Re-boiling clean uncontaminated drinking will water not cause cancer or any other health problems. However, boiling water contaminated with chemicals such as nitrates or toxic elements such as arsenic...will actually increase the concentration...consuming water contaminated with nitrates can cause a blood disorder called methemoglobinemia...cancer...arsenic poisoning...the levels of both nitrates and arsenic are regulated...monitored in towns and cities...if water comes from a city water source, it is safe...if you have a private well and the levels of these contaminants are too high, you must install a water filtration system..."

So there may be some truth after all in the old folks saying about not reboiling drinking water...

Maybe in the old time when people were using water from well, or when the quality of tap water was not as well regulated, there was this need to minimize the concentration of harmful chemicals in the water by not reboiling it. But perhaps the same logic is less relevant applying to today's world, where the State generally provides tap water safe enough for daily consumption, and most families nowadays have installed water filter system in their home. Like my home, we have 2 water filters, one for outdoor filtration, one for the kitchen.

But to avoid being nagged by grandma and dad, I think it's better for me to avoid adding new water to the thermo pot when they are around. Or maybe I should consider grandma's advise to empty the thermo pot every time before adding new water? :)