Safe water temperature for mixing formula

Updated 3 months ago

Why water temperature matters

Water temperature when preparing formula affects two things: safety and nutrition. Water that is too cool may not kill bacteria that can be present in powdered formula or tap water. Water that is too hot can destroy heat-sensitive nutrients — particularly some vitamins — and can make the formula too hot to feed safely.

The correct temperature is a balance between both — hot enough to be safe, cool enough to preserve nutrients and be comfortable for your baby.

Should I boil the water?

Yes — for babies under 12 months, boiling the water before preparing formula is recommended. Boiling kills bacteria that may be present in the water supply or in the formula powder itself, including Cronobacter sakazakii, a rare but serious pathogen that can occasionally be found in powdered formula.

Boil fresh water and allow it to cool before mixing with formula powder — do not use water that has already been boiled previously, as repeated boiling can concentrate minerals.

What temperature should the water be?

The recommended water temperature for mixing formula is between 40°C and 50°C (104°F–122°F) — warm but not boiling. At this temperature, the water is hot enough to dissolve the powder completely and reduce bacterial risk, but cool enough to preserve heat-sensitive nutrients.

Always check the preparation instructions on the tin of the formula you are using — some brands specify a slightly different temperature range. Always follow the manufacturer’s guidance.

How to cool boiled water to the right temperature

• Boil fresh water and pour the required amount into a sterilised bottle
• Leave to cool for approximately 30 minutes — this typically brings the temperature to around 40–50°C
• If in doubt, use a thermometer to check — formula thermometers are inexpensive and widely available
• Alternatively, use a temperature-controlled kettle set to 50°C if available

Can I use bottled water?

Bottled water can be used if tap water quality is a concern — for example when travelling. Choose a still water with a low mineral content (sodium below 200mg/L, fluoride below 1.5mg/L). Even bottled water should be boiled before use for babies under 12 months, as it is not sterile.

Do not use artificially softened water, sparkling water or water with added minerals or flavourings.

Quick reference

• Boil first? Yes — always use freshly boiled water
• Mixing temperature — 40–50°C (104–122°F)
• Cooling time — approximately 30 minutes after boiling
• Bottled water — still, low mineral, boil before use
• Never use — softened water, sparkling water, previously boiled water, or water straight from the hot tap