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 could have heard that boiling water greater than as soon as will in some way make the water dangerous and due to this fact you must 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 akin to arsenic, or salts akin to nitrates and fluoride.
This isn’t true. To know 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 equipped by Sydney Water, Australia’s largest water utility which provides water to Sydney, the Blue Mountains and the Illawarra area.
From the publicly obtainable knowledge for the January to March 2025 quarter for the Illawarra area, these have been the typical water high quality outcomes:
pH was barely alkaline
whole 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 “mushy” water with a complete hardness worth under 40mg of calcium carbonate per litre.
The water contained hint quantities of metals akin to iron and lead, low sufficient magnesium ranges that it may’t be tasted, and sodium ranges considerably decrease than these in well-liked mushy drinks.
These and all different monitored high quality parameters have been effectively throughout the Australian Consuming Water Tips throughout that interval. When you 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 have to evaporate a few 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 unstable natural compounds would possibly escape into the air, however the quantity of the inorganic compounds (akin to metals and salts) stays unchanged.
Whereas the focus of inorganic compounds would possibly enhance as consuming water evaporates when boiled, proof exhibits it doesn’t occur 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 throughout the limits of Australian tips.
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 can be small, and the fluoride content material in every cup of tea can be related.
However let’s assume that when making the second cup, you let the water hold boiling till 100ml of what’s within the kettle evaporates. Even then, the quantity of fluoride you’ll eat 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 equipped water could have contained. Let’s take lead: the water equipped within the Illawarra area as talked about above, had a lead focus of lower than 0.0001mg per litre. To achieve an unsafe lead focus (0.01mg per litre, based on Australian tips) in a cup of water, you’d have to boil down roughly 20 litres of faucet water to simply that cup of 200ml.
Virtually that’s unlikely to occur – most electrical kettles are designed to boil briefly earlier than robotically shutting off. So long as the water you’re utilizing is throughout the tips for consuming water, you possibly can’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 quite a lot of different components that contribute to the style of your faucet water.
The underside line is that so long as the water in your kettle was initially compliant with tips for secure consuming water, it’s going to stay secure and potable even after repeated boiling.
Faisal Hai, Professor and Head of Faculty of Civil, Mining, Environmental and Architectural Engineering, College of Wollongong
This text is republished from The Dialog beneath a Artistic Commons license. Learn the unique article.
