How long do I leave boiled kettle water for formula so it stays 70C?

What is the NHS 70C / 30-minute kettle rule?

Powdered infant formula is not sterile. The NHS making-up baby formula page and Best Start in Life both give the same water step: fill the kettle with at least 1 litre of fresh tap water from the cold tap, boil it, then leave that water to cool in the kettle for no more than 30 minutes so it remains at a temperature of at least 70C.

Those two numbers — 70C and 30 minutes after a 1-litre boil — are NHS figures. This page does not add a home thermometer chart or a shorter cool-down for a half-full kettle.

How do I run the kettle with a timer so the water stays 70C?

1. 1
   Empty and refill Empty the kettle. Fill it with at least 1 litre of fresh cold tap water. Do not top up leftover boiled water.
2. 2
   Boil, then start a 30-minute timer Boil the kettle. When it switches off, start a timer for 30 minutes. NHS: leave the water to cool in the kettle for no more than those 30 minutes.
3. 3
   Make the feed inside that window Clean and disinfect the surface, wash your hands, and use a sterilised bottle. Pour the amount of water the tin asks for into the bottle first, while it is still hot. Add level scoops with the tin’s own scoop.
4. 4
   Cool the feed, not the kettle water, for drinking Screw on the ring, cap the teat, shake until the powder dissolves. NHS: cool the bottle (lid on) under cold running water so the feed is not too hot to drink. Test on the inside of your wrist.
5. 5
   If 30 minutes have already passed Do not guess a new temperature. Boil a fresh litre and start the 30-minute window again. This page does not publish a ‘still 70C after 40 minutes’ figure.

NCT’s step-by-step formula guide cites the same NHS boil-and-cool: at least 1 litre of fresh tap water, then no more than half an hour, so the water is still at the required 70C when the powder goes in.

Do I need a formula prep machine to hit 70C?

The NHS kettle steps are written for a household kettle. A prep machine is optional kit, not the official method. If you already have a machine, NHS says to make sure the water that comes out is at least 70C when it is mixed with the powder, and that you can check with a digital food thermometer. If the water is less than 70C, NHS says to stop using the machine and follow the kettle guide instead.

Which? and NCT both discuss machines and baby kettles as gadgets parents buy to skip the wait. The temperature rule those reviews are measured against is still the NHS 70C figure, not a machine’s marketing claim. First Steps Nutrition Trust, cited by NCT, treats a normal kettle used to the NHS steps as the route that matches the guidance.

Can I use a shorter cool-down if I only boiled 500ml?

The national NHS pages you should follow for this query state at least 1 litre and no more than 30 minutes. They do not print a second official cool-down for a smaller boil. Some local leaflets have used other pairings. Those are not the national NHS 70C / 30-minute rule this page cites, and this page does not invent a 15-minute or 40C figure.

• Previously boiled water. NHS: do not use it. Minerals concentrate if you keep re-boiling the same water.
• Artificially softened water. NHS: do not use it for formula.
• Bottled water. NHS does not treat it as the default; it may contain too much sodium or sulphate. Use fresh tap water unless a health visitor has given you other advice.
• Microwave to reheat a feed. NHS: do not, because of hot spots.

In shortIn short: a kettle, a litre of fresh tap water, a 30-minute ceiling after the boil, and water still at least 70C when it meets the powder. That is the NHS rule. A prep machine is not required to follow it. If a machine’s water is under 70C, NHS says to go back to the kettle steps.