Safe formula comes down to four things: clean hands and sterilised equipment, the exact water-to-powder ratio on the label, the right water for where you live, and not keeping made-up milk too long. Put the water in the bottle first, then add loose, level scoops of powder using the scoop from that tin. Make each feed fresh when you can. A made-up feed can go in the fridge at 5°C or colder for up to 24 hours, and anything your baby leaves is thrown away.
The one step that really differs by country is the water temperature. The NHS and WHO mix powder with water that is still at least 70°C. Australian government guidance cools boiled water to lukewarm first. The CDC in the US says safe tap water is usually fine, with a hot-water step for babies at higher risk. This guide sets out each version side by side so you can follow the one your health service uses.
Why does formula preparation differ between countries?
Powdered formula is not sterile. The NHS guide to making up formula says sealed tins and packets can still contain bacteria, and that water at 70°C or more kills them. WHO's guidelines on powdered infant formula take the same approach for all babies.
Other health services weigh that risk differently against the risk of scalds and the practicalities of home preparation. The result is a few different, legitimate methods:
| Who | Water for mixing | Made-up feed in the fridge | Out of the fridge |
|---|---|---|---|
| Australia (government) | Boiled, cooled to lukewarm | Up to 24 h at 5°C or below | Discard after 1 hour |
| UK (NHS) | Boiled, still at least 70°C | Use within 24 h | Use within 2 hours |
| US (CDC) | Safe tap water; boiled for higher-risk babies | Use within 24 h | 2 h from making, 1 h from starting |
| WHO | Boiled, at least 70°C | Up to 24 h at 5°C or below | Discard after 2 hours |
Specialist formulas and hospital feeding plans can have their own instructions. If your baby has one, follow the plan your team gave you.
How do you make up a bottle of formula, step by step?
These steps are the parts every source agrees on, with the water step split by region below.
- Clean and prepare. Clean the surface, wash your hands and use bottles and teats that have been cleaned and sterilised.
- Prepare the water using your region's method (see the next section).
- Water first. Pour the amount of water the label says into the bottle and check the level at eye height.
- Measure the powder. Use only the scoop that comes with that formula. Fill it loosely and level it with a clean, dry knife or the leveller provided. Don't pack it down.
- Mix. Put the teat and cap on and shake until the powder has dissolved.
- Cool and test. Cool the bottle under cold running water with the lid on, then shake a few drops onto the inside of your wrist. It should feel warm or cool, not hot.
- Feed, then discard. Throw away anything left in the bottle after the feed.
The Better Health Channel from Victoria, Australia adds: never use a half scoop, use the powder within one month of opening the tin, and make one bottle at a time. It also says to sterilise all bottle-feeding equipment until 12 months, for example with 5 minutes of rapid boiling. The CDC's guide to cleaning feeding items asks for sanitising at least daily, especially for babies under 2 months, premature babies or those with weakened immunity. Bottle-feeding basics covers cleaning in more detail.
Australia
The Australian Government's Pregnancy, Birth and Baby guide to making formula says to boil fresh tap water in a kettle or on the stove and let it cool to room temperature or lukewarm. The Australian Better Health Channel says cooling to lukewarm takes at least 30 minutes. Australia's Pregnancy, Birth and Baby also says sealed bottles of this cooled boiled water can be stored in the fridge for up to 24 hours, ready for the powder.
UK and WHO
The NHS says to fill the kettle with at least 1 litre of fresh tap water (not water that's been boiled before), boil it, and leave it no more than 30 minutes so it's still at least 70°C. Pour it in while hot, add the powder, then cool the bottle before feeding. WHO's guideline uses the same 70°C and 30-minute limits and says bottled water also has to be boiled because it isn't sterile.
The NHS says formula preparation machines are fine only if the water reaches at least 70°C once mixed with the powder. If it doesn't, stop using the machine.
US
The CDC's formula preparation guide says water from a safe source, including filtered or unfiltered tap water, is generally fine. For babies under 2 months, born before 37 weeks or with a weakened immune system, it says to boil the water and wait about 5 minutes before mixing, because very hot water (around 70°C or 158°F) is needed to kill germs such as Cronobacter. The AAP's guide to preparing formula with water gives the same advice for the same groups.
Which water is safe for baby formula?
- Tap water is the usual choice in all three countries: boiled in Australia and the UK, and from a safe source in the US.
- Water boiled before or artificially softened water shouldn't be used, according to the NHS.
- Bottled water isn't usually recommended by the NHS because it isn't sterile and can be high in sodium or sulphate. It can be used when tap water is unavailable or contaminated.
- During an emergency such as a flood, the CDC says to use bottled water if tap water may be unsafe, or boil it and let it cool. Boiling doesn't remove chemical contamination, so use bottled water or ready-to-feed formula then.
If you're not on town water (for example tank or bore water), ask your local health service which water to use.
How long does made-up formula last?
The safest feed is one made just before your baby needs it. When that isn't practical, these limits apply:
- In the fridge: up to 24 hours. Australia's Pregnancy, Birth and Baby and WHO specify 5°C or colder, and the NHS and the CDC also give 24 hours.
- At room temperature: Australian government guidance says discard after more than 1 hour. The NHS's formula questions page and WHO say use within 2 hours. The CDC says within 2 hours of making it and within 1 hour of your baby starting to drink.
- In a cool bag with an ice pack: the NHS says use within 4 hours. WHO says 2 hours, because cool bags don't always keep feeds cold enough.
- Leftovers: every source says to throw away milk your baby doesn't finish. The CDC explains that saliva in the bottle lets bacteria grow.
WHO says to rewarm a stored feed for no more than 15 minutes, shaking it now and then so it heats evenly. Never use a microwave: the NHS, CDC and WHO all warn it heats unevenly and can scald your baby's mouth. Australia's Better Health Channel suggests standing the bottle in hot (not boiling) water for about 10 minutes, then testing it on your wrist.
Opened powder keeps for about one month (check the label) in a cool, dry place with the lid closed. The CDC says not to refrigerate it. The AAP says opened ready-to-feed or liquid concentrate should be covered, refrigerated and used within 48 hours.
What are the safest options for night feeds and travel?
Night feeds are when shortcuts are most tempting. Safer options include:
- Ready-to-feed liquid formula. The NHS suggests it when you can't make up a feed on the go, and many families keep some for the hardest feeds of the night.
- Make-ahead bottles in the fridge, used within 24 hours and warmed just before feeding.
- In Australia, sealed bottles of cooled boiled water in the fridge, with the powder added at feed time.
For travel, the NHS suggests carrying a measured amount of powder in a clean, dry container, an empty sterilised bottle, and a full, sealed vacuum flask of just-boiled water, which stays above 70°C for several hours. In Australia, Better Health Channel likewise suggests carrying hot water and powder separately and mixing just before the feed. If you take a made-up feed, chill it in the fridge first and carry it in a cool bag with an ice pack. See travelling with a baby for more.
What are the most common formula mistakes?
- Adding an extra scoop to "fill them up". The NHS says extra powder can cause constipation or dehydration.
- Watering formula down to make it last. The AAP says this lowers nutrients, slows growth and can upset the body's salt balance badly enough to cause seizures. If money is tight, talk to your GP or child-health nurse or a local family support service.
- Packed or heaped scoops, half scoops, or using a scoop from another brand.
- Adding powder before the water. The CDC says always measure the water first.
- Adding cereal, sugar or anything else to a bottle. The NHS says not to.
- Keeping leftovers for the next feed.
- Microwaving bottles.
How much to offer is a separate question; see how much formula. For holding the bottle and letting your baby set the pace, see paced bottle feeding.
When should you get help?
Formula made too strong or too weak, or a baby who is unwell and not feeding well, can lead to dehydration. The NHS dehydration page lists the signs and how urgent each is.
The RCH dehydration fact sheet treats sunken eyes as severe dehydration that needs hospital care fast. The NHS dehydration page gives a sunken soft spot an urgent GP appointment, but we use the stricter tier.
Get medical advice the same day (your GP or a health advice line (Pregnancy, Birth and Baby on 1800 882 436 in Australia, NHS 111 in the UK, your pediatrician's after-hours line in the US)) if your baby:
- has fewer wet nappies than usual or dark yellow wee
- seems irritable, or has few tears when crying
- is vomiting feeds or refusing feeds and seems unwell
Mention it at the next check with your GP or child-health nurse if you're unsure how much to offer, your baby seems constipated, you're thinking of changing formula, or you realise feeds have been made up wrongly and your baby seems well.
What to note when someone else makes the bottles
If a partner, grandparent or carer helps, write down the brand, the number of scoops for each amount of water, and the water method you use. Noting the time a bottle was made and the time the feed started makes the 1-hour or 2-hour limit easy to follow. It also gives your GP or child-health nurse something concrete to look at if feeding becomes a worry.
