The kettle is a family staple virtually in all places – how else would we make our scorching drinks?
However is it okay to re-boil water that’s already within the kettle from final time? Whereas bringing water to a boil disinfects it, you might have heard that boiling water greater than as soon as will somehow make the water harmful and due to this fact you need to empty the kettle every time.
Such claims are sometimes accompanied by the argument that re-boiled water results in the buildup of allegedly hazardous substances together with metals corresponding to arsenic, or salts corresponding to nitrates and fluoride.
This isn’t true. To grasp why, let’s have a look at what’s in our faucet water and what actually occurs after we boil it.
What’s in our faucet water?
Let’s take the instance of faucet water provided by Sydney Water, Australia’s largest water utility which provides water to Sydney, the Blue Mountains and the Illawarra area.
From the publicly available data for the January to March 2025 quarter for the Illawarra area, these have been the typical water high quality outcomes:
- pH was barely alkaline
- complete dissolved solids have been low sufficient to keep away from inflicting scaling in pipes or home equipment
- fluoride content material was applicable to enhance dental well being, and
- it was “soft” water with a complete hardness worth beneath 40mg of calcium carbonate per litre.
The water contained hint quantities of metals corresponding to iron and lead, low sufficient magnesium ranges that it might’t be tasted, and sodium ranges considerably decrease than these in common soft drinks.
These and all different monitored high quality parameters have been nicely inside the Australian Drinking Water Guidelines throughout that interval. For those who have been to make tea with this water, re-boiling wouldn’t trigger a well being downside. Right here’s why.
It’s tough to pay attention such low ranges of chemical substances
To pay attention substances within the water, you’d must evaporate a number of the liquid whereas the chemical substances keep behind. Water evaporates at any temperature, however the overwhelming majority of evaporation occurs on the boiling level – when water turns into steam.
Throughout boiling, some volatile organic compounds may escape into the air, however the quantity of the inorganic compounds (corresponding to metals and salts) stays unchanged.
Whereas the focus of inorganic compounds may improve as consuming water evaporates when boiled, proof reveals it doesn’t happen to such an extent that it will be hazardous.
Let’s say you boil one litre of faucet water in a kettle within the morning, and your faucet water has a fluoride content material of 1mg per litre, which is inside the limits of Australian pointers.
You make a cup of tea taking 200ml of the boiled water. You then make one other cup of tea within the afternoon by re-boiling the remaining water.
On each events, if heating was stopped quickly after boiling began, the lack of water by evaporation could be small, and the fluoride content material in every cup of tea could be comparable.
However let’s assume that when making the second cup, you let the water maintain boiling till 100ml of what’s within the kettle evaporates. Even then, the quantity of fluoride you’ll devour with the second cup (0.23mg) wouldn’t be considerably increased than the fluoride you consumed with the primary cup of tea (0.20mg).
The identical applies to every other minerals or organics the provided water could have contained. Let’s take lead: the water provided within the Illawarra area as talked about above, had a lead focus of lower than 0.0001mg per litre. To succeed in an unsafe lead focus (0.01mg per litre, in response to Australian pointers) in a cup of water, you’d must boil down roughly 20 litres of faucet water to only that cup of 200ml.
Virtually that’s unlikely to occur – most electrical kettles are designed to boil briefly earlier than routinely shutting off. So long as the water you’re utilizing is inside the pointers for consuming water, you may’t actually focus it to dangerous ranges inside your kettle.
However what about style?
Whether or not re-boiled water really impacts the style of your drinks will rely solely on the specifics of your native water provide and your private preferences.
The slight change in mineral focus, or the lack of dissolved oxygen from water throughout boiling could have an effect on the style for some individuals – though there are a number of different components that contribute to the taste of your tap water.
The underside line is that so long as the water in your kettle was initially compliant with pointers for protected consuming water, it’ll stay protected and potable even after repeated boiling.
- Faisal Hai, Professor and Head of College of Civil, Mining, Environmental and Architectural Engineering, University of Wollongong
This text is republished from The Conversation underneath a Inventive Commons license. Learn the original article.
