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How do you make up baby formula safely? What the NHS says, and what we used

The NHS website's guide says to use freshly boiled tap water that has cooled for no more than 30 minutes so it is still at least 70C, to put the water in the bottle first and then the powder, and to test the temperature on your wrist before feeding.[1]

By Tom, a dad of two in Kent. Published 3 October 2026. NHS pages last checked 3 October 2026.

How this page works. Every health fact here comes from the NHS website and links to the page it came from, with that page's review date. The "In our house" box is our own experience. Nothing here is advice. For advice, go to the NHS page, your health visitor, or your GP.

Why the NHS stresses hygiene

A baby's immune system is not as strong as an adult's, so the NHS says bottles, teats, and other feeding equipment need to be washed and sterilised before each feed. This reduces the chance of an infection, in particular diarrhoea and vomiting.[1]

Even sealed tins and packets of powdered formula can sometimes contain bacteria. Bacteria multiply very fast at room temperature, and in a fridge they can still survive and multiply, only more slowly. So the NHS says it is best to make up feeds one at a time, as your baby needs them.[1]

The steps, in brief

These are the NHS website's steps, summarised:[1]

  1. Fill the kettle with at least 1 litre of fresh tap water. Do not use water that has been boiled before.[1]
  2. Boil the water, then leave it to cool for no more than 30 minutes, so that it stays at a temperature of at least 70C.[1]
  3. Clean and disinfect the surface you will use, and wash your hands.[1]
  4. Following the manufacturer's instructions, pour the amount of water you need into the bottle first, while it is still hot, and double check the level.[1]
  5. Loosely fill the scoop that comes with that formula and level it with the leveller or the flat edge of a clean, dry knife. Different formulas come with different scoops.[1]
  6. Fit the teat and ring firmly, cover the teat with the cap, and shake until the powder has dissolved.[1]
  7. Cool the feed by holding the bottle, with the lid on, under cold running water.[1]
  8. Test the temperature on the inside of your wrist before feeding. The NHS says it should be body temperature, which means it feels warm or cool, but not hot.[1]
  9. Throw away any made-up formula left in the bottle after a feed.[1]

If you use a cold-water steriliser, the NHS page also says to shake off any excess solution from the bottle and teat, or rinse them with cooled boiled water from the kettle, not tap water.[1]

Dos and don'ts

The NHS page lists these dos and don'ts:[1]

  • Follow the manufacturer's instructions very carefully, because the amounts of water and powder vary.[1]
  • Do not add extra powder. The NHS says this can make your baby constipated or dehydrated.[1]
  • Do not add extra water. Too little powder may not give your baby enough nourishment.[1]
  • Do not add sugar or cereals to formula.[1]
  • Never warm up formula in a microwave. The NHS says it may heat the feed unevenly and burn your baby's mouth.[1]

What about bottled water?

The NHS says bottled water is not usually recommended for making up formula, because it is not sterile and may contain too much salt (sodium) or sulphate. In rare circumstances, such as when drinking water is unavailable or has been contaminated, it can be used. The page says to still follow its step-by-step guide and any additional advice from the Food Standards Agency or the UK Health Security Agency.[1]

What about formula preparation machines?

The NHS website says that if you use a baby formula preparation machine, you follow the manufacturer's instructions and make sure the water that comes out is at least 70C when it is mixed with the powder. It says you can use a digital food thermometer to check, and that if the water is less than 70C you stop using the machine and follow the step-by-step guide instead.[1]

Not every NHS page says the same thing. Just One Norfolk, a service run by East of England Community Health and Care NHS Trust, says the NHS advises against using formula preparation machines, because they deliver a small shot of very hot water and then add cool water, which it says will not kill the bacteria in formula milk effectively.[2] We link to both so you can read each one for yourself.

In our house

We used a Tommee Tippee Perfect Prep machine to make up formula. In the early days we checked the temperature of the water from the machine, and after that we trusted it. We are aware that some NHS trusts do not recommend formula machines, and, as above, the NHS website's page sets out a 70C check for anyone who uses one. Because we had the machine, we did not make bottles up in advance, and a made-up feed never sat for more than an hour. When we left the house and might need a feed, we took boiled water in flasks, so we never needed bottled water. We used standard formula only, with no follow-on milk, until each of our children turned one, and then moved them to full-fat cows' milk. This is what we did, not a recommendation. If you are deciding, the two NHS pages linked here are the place to read.

If you are worried

This page is a summary of NHS information plus our own experience. It is not medical advice. If you are worried about your baby, the NHS has a page on diarrhoea and vomiting, and you can speak to your health visitor or GP, or use NHS 111.

Sources

  1. NHS website: How to make up baby formula. Page last reviewed 31 August 2023; next review due 31 August 2026 (that date has passed); page last updated by the NHS on 20 April 2026. I checked it on 3 October 2026.
  2. Just One Norfolk (East of England Community Health and Care NHS Trust): Preparing and storing feeds. A local NHS service page, not the national NHS website. It shows no review date. I checked it on 3 October 2026.

The NHS lists a next review date that has passed for: How to make up baby formula. The page may have been updated since, so check the live page.

Contains public sector information licensed under the Open Government Licence v3.0. This page summarises NHS website content in our own words, and an adaptation may not carry the NHS's formal clinical approval. Tiny Tummies is not affiliated with or endorsed by the NHS.

About the author

I am Tom, a dad of two in Kent. When I wrote this, our children were 3 years 9 months and 16 months old. I am not a clinician, and nothing here is medical advice. I also built Tiny Tummies, a baby feeding tracker. I use AI tools to help draft these pages. Every health fact is checked against the NHS page it links to, and the "In our house" boxes are what my wife and I actually did.