Guwahati, July 20 -- Faisal Hai, University of Wollongong

The kettle is a household staple practically everywhere - how else would we make our hot drinks?

But is it okay to re-boil water that's already in the kettle from last time? While bringing water to a boil disinfects it, you may have heard that boiling water more than once will somehow make the water harmful and therefore you should empty the kettle each time.

Such claims are often accompanied by the argument that re-boiled water leads to the accumulation of allegedly hazardous substances including metals such as arsenic, or salts such as nitrates and fluoride.

This isn't true. To understand why, let's look at what is in our tap water and what really happens when we boil it.

Le...