How to Prepare Baby Formula Safely - What the WHO, FDA, and Manufacturer Instructions Agree On

Preparing infant formula looks simple, powder, water, bottle, baby. The reason the WHO, CDC, FDA, and essentially every pediatrician in the developed world have detailed preparation guidelines is that the few variables involved (water temperature, timing, equipment cleanliness, storage) cumulate into real safety differences. Properly prepared formula has Cronobacter contamination risk close to zero. Improperly prepared formula is where the real-world infant illness cases actually come from, more often than from the formula itself.

This article walks through what the international guidance actually says, where the major bodies agree and disagree, and what the practical implementation looks like for a US parent.

The five principles that matter

Across WHO, CDC, FDA, and AAP guidance, the consistent safety principles for formula preparation are:

1. Wash hands and sterilize equipment. Hands, bottles, nipples, scoops, counter surface. The first source of contamination is environmental, not the formula.
2. Use hot enough water to kill bacteria. The WHO recommends water at least 70°C (158°F) for preparing powdered infant formula. This is the single most important rule.
3. Prepare each bottle fresh. Don't batch multiple bottles and refrigerate; don't keep prepared formula at room temperature for extended periods.
4. Cool quickly and feed promptly. Once the formula is mixed, cool to feeding temperature rapidly (running cold water over the bottle) and feed within 2 hours, or refrigerate for up to 24 hours.
5. Discard unused formula after feeding. If a baby doesn't finish a bottle, the remaining liquid must be discarded within 1 hour. Don't "save for later."

These five principles cover 95% of the safety envelope. Specific implementation details below.

The 70°C / 158°F water rule (the most-violated one)

WHO Guideline 4 of the 2007 Safe Preparation guidance: water for preparing powdered infant formula should be "at least 70°C", hot enough to kill Cronobacter sakazakii (which is the bacteria at the center of the 2022 Abbott/Similac recall crisis) and other heat-sensitive pathogens that may contaminate powdered formula.

The CDC and AAP repeat this guidance. The FDA's Cronobacter guidance references the 70°C standard.

Why 70°C specifically? Below that temperature, Cronobacter sakazakii can survive in the prepared formula and grow as the bottle cools. Above 70°C, the bacteria are reliably killed within seconds. The WHO chose 70°C as the tradeoff between sufficient kill time and practical cooling-to-feeding-temperature timelines.

Practical implementation:

• Boil water, then let it cool to roughly 70-80°C (158-176°F). One common approach: boil, let sit 30 minutes.
• Measure with a thermometer the first few times to calibrate. Kitchen instant-read thermometers work.
• Do NOT use lukewarm water. Room-temperature water, or worse, refrigerator water, cannot kill Cronobacter.
• Do NOT microwave the water or the prepared bottle. Microwave heating is uneven and creates hot spots that can burn the baby's mouth.

Why some brands push back on 70°C

Several manufacturer brands publish preparation instructions with lower water temperatures (typically 40-60°C / 104-140°F). The justification they give is typically "preserve heat-sensitive nutrients and probiotics."

This is a real tradeoff but it's not how most pediatricians and public health authorities resolve it. The WHO explicitly addresses this: "While nutrient losses are possible at 70°C, the risk of Cronobacter survival at lower temperatures is a greater clinical concern. Use 70°C."

For probiotic-containing formulas specifically (HiPP Combiotik, Kendamil Organic, Gerber Good Start GentlePro, Nutramigen with Enflora LGG): 70°C water will kill most of the live probiotic cultures. Parents and pediatricians can weigh the microbial trade-off, but the safe side of the tradeoff is clearly 70°C. If you want maximum probiotic survival, choose a formula that delivers probiotics in a sprinkle/capsule format separate from the reconstitution step.

Water source: what to actually use

The water you use matters more than you might think:

Tap water

Acceptable in most US municipal water supplies if boiled first (per the 70°C rule). Municipal tap water in most of the US is safe for infant formula preparation after boiling.

Exceptions:

• Fluoride content. Many US municipal water supplies add fluoride. For infants under 6 months, the FDA and ADA recommend using non-fluoridated or low-fluoride water for formula preparation to avoid potential fluorosis. AAP guidance on fluoride exposure in infancy.
• Lead concerns. If you live in a US area with lead service lines or old plumbing, tap water may contain lead. Let the water run several minutes before collecting, or use filtered water.
• Well water. Should be tested annually for nitrates, coliform, and other contaminants. Some well-water minerals interact poorly with formula composition.

Filtered water

Acceptable for US homes. A quality carbon filter (Brita, PUR) reduces chlorine taste and some contaminants. Reverse-osmosis filtration is more thorough but removes minerals (some of which are desirable for baby's development).

Distilled water

Pros: No fluoride, no contaminants, consistent mineral-free baseline. Cons: Lacks some trace minerals; needs extra attention to re-mineralization via the formula's own composition.

Bottled water

Many parents use bottled water for formula preparation. Bottled water is regulated by FDA (not EPA); safety standards are similar to tap water. Look for "distilled," "purified," or labels indicating below 0.3 ppm fluoride specifically marketed for infant formula preparation.

Never use

• Mineral water / spring water with high mineral content. Excess sodium, magnesium, or sulfate can affect infant kidneys.
• Warm or hot tap water (may leach lead from plumbing).
• Water that has been sitting in a kettle or reservoir for extended periods.

The preparation sequence

The WHO-standard sequence:

1. Wash your hands thoroughly with soap and water.
2. Clean and sanitize all equipment, bottle, nipple, scoop, ring, cap, and preparation surface. Hot-water boil sanitization (5 minutes of rolling boil) or a UV sterilizer both work. For the first few months, sterilize between every use.
3. Boil fresh water for at least 1 minute. Let cool to 70-80°C (158-176°F). Don't use water that has been sitting in the kettle for hours.
4. Pour the hot water into the clean bottle first. Always water before powder.
5. Add the exact amount of powder using the manufacturer's scoop (NEVER improvise the scoop size). Check the manufacturer's powder-to-water ratio, this varies between brands (most US brands use 1 scoop per 2 fl oz water; most European brands use 1 scoop per 30 ml water).
6. Cap and shake until fully dissolved. A few minutes of gentle shaking.
7. Cool to feeding temperature by running cold water over the outside of the bottle. DO NOT submerge the bottle cap in water. Aim for ~37°C (98-99°F) for comfortable infant feeding.
8. Test temperature on the inside of your wrist before offering.
9. Feed within 2 hours of preparation. Discard unused formula within 1 hour of feeding start.

Storage rules

Unopened tins:

• Cool, dry, stable temperature. Room temp is fine.
• Do not freeze (condensation will damage the powder when tin returns to room temp).
• Check the printed expiration date on arrival.

Opened tins:

• Use within the window specified by the manufacturer, typically 3-4 weeks for HiPP, Holle, Kendamil; 4 weeks for Similac and Enfamil.
• Keep the tin tightly sealed between uses.
• Store in a dry cupboard at room temperature. Do NOT refrigerate (the tin will develop condensation inside, which damages the powder).

Prepared bottles:

• Feed immediately when possible.
• If refrigeration is needed: cool rapidly within 30 minutes of preparation, then refrigerate at 4°C (40°F) or below for up to 24 hours.
• Reheat refrigerated bottle by placing in warm (not hot) water. Do NOT microwave.
• Discard any refrigerated bottle not consumed within 24 hours.

Unused formula after feeding:

• If a baby doesn't finish a bottle, discard within 1 hour of feeding start. Saliva introduces bacteria that grow rapidly in leftover formula.

Traveling / on-the-go:

• For short trips (< 2 hours): prepare at home, transport in insulated bottle bag.
• For longer trips: bring measured powder in a formula dispenser and pre-boiled water in a thermos. Mix on-site.
• Ready-to-feed liquid formula is the safest for travel but much more expensive per feed.

The 2022 Cronobacter crisis: what parents should take away

The February 2022 Abbott/Similac recall exposed real gaps in Cronobacter sakazakii control at one specific manufacturing facility. Since then:

• FDA has increased inspection frequency at powdered formula facilities.
• Manufacturers have expanded Cronobacter testing in quality control.
• Preparation practices at home matter more than ever, even if a tin is contaminated at low levels, proper preparation (70°C water, sterile equipment, fresh preparation) kills the bacteria before baby feeds.

The lesson for parents: the 70°C water rule isn't abstract. It's the one step that converts a possibly-contaminated powder into a safe bottle. Skipping it means relying on the manufacturer's QC being perfect, which the 2022 crisis shows isn't always the case.

For the full recall context, see the FDA 21 CFR 107 outer pillar and our Similac brand page.

A note on ready-to-feed liquid formula

Ready-to-feed (RTF) formula bypasses the preparation step entirely. The liquid is sterile at the point of manufacture and doesn't require 70°C reconstitution. For parents concerned about preparation safety, or for specific situations (travel, overnight, medically fragile infants) — RTF is the safer option.

Cost: typically 2-3x per ounce vs powdered formula. Most major brands (Similac, Enfamil, Kendamil, Bobbie) offer RTF versions; most European organic imports (HiPP, Holle, Lebenswert, Loulouka) do not, the RTF market is primarily US-domestic.

FAQ

Primary sources

1. WHO Safe Preparation, Storage and Handling of Powdered Infant Formula (Guidelines), the canonical international guidance. who.int
2. CDC Cronobacter Prevention and Formula Preparation Guidelines. cdc.gov
3. FDA Guidance on Cronobacter Contamination in Powdered Infant Formula. fda.gov
4. AAP Clinical Report on Fluoride Exposure in Infancy. aap.org

This site provides research and comparisons, not medical advice. Consult your pediatrician before changing your baby's formula.

Related reading

• Do I need to sterilize baby bottles every time I use them?
• Is formula powder safe at room temperature?
• Powder Infant Formula Shelf Life — The Science of Why It Expires
• Prepared Bottle Reheating — The Science of Why Microwaves Are Banned
• Formula Water Temperature — The Science Behind 70°C and Cronobacter Protection