For most families in Ireland, water from a well maintained reverse osmosis (RO) system can be used to make up baby formula. You should still boil it and make the bottle with water that is at least 70°C, as the HSE advises. Formula is made to give your baby the nutrients they need, so the water simply needs to be clean and low in added salts.
Why does the water in a baby's bottle matter so much?
If your baby is formula fed, water makes up most of every bottle. And babies drink a lot for their size. The HSE guide to preparing baby formula says a baby needs about 150ml of formula per kilo of body weight each day.
That means a baby of 5kg may take around 750ml a day. For an adult, the same ratio would be many litres. So the quality of that water matters.
Health authorities also take extra care with infants. Their bodies are small and still growing. This is why official advice on formula is so precise.
What does the evidence say about Irish tap water?
The good news first. The EPA report on Drinking Water Quality in Public Supplies 2025 found that 99.8% of samples met microbiological limits. Chemical standards were met in 99.7% of samples. Public water in Ireland is safe to drink.
The same report shows why some parents still want an extra layer of care. In 2025, there were 66 boil water notices. Around 200,000 people were affected by boil water notices or water restrictions. Twenty four supplies had failures for E. coli or Enterococci. Another 24 supplies had failures for trihalomethanes, which can form when chlorine reacts with natural matter in water.
Lead is the other concern. Lead pipes were used in homes up to and including the 1970s. Uisce Éireann has replaced or ruled out 72,000 public lead connections, from an estimated 180,000. Pipes inside your own home are a separate matter, and many older houses may still have them.
None of this is a reason for alarm. But it does explain why many parents look closely at the water they use for feeds.
What is RO water, in simple terms?
Reverse osmosis pushes water through a very fine membrane. This membrane holds back many dissolved substances. These can include lead, nitrates and much of the taste and smell of chlorine.
It also removes most of the natural minerals and salts in water. Some parents worry about this. For bottle feeds, it is usually not a problem, and here is why.
Is RO water safe for making up baby formula?
In general, yes. Infant formula is carefully made to give your baby the nutrients they need. The water is not there to add minerals. Its job is to be clean.
In fact, official advice leans towards water that is low in minerals. The Food Safety Authority of Ireland says it is best not to use bottled water labelled "Natural Mineral Water" for formula. This is because it can have higher levels of sodium and other minerals.
Water from a working RO system is low in these salts. That makes it a sensible base for a bottle. Just be sure to follow the formula label exactly. Too much or too little water changes what your baby receives.
Do I still need to boil RO water for a baby's bottle?
Yes. Powdered formula is not sterile. The HSE advises that you boil the water and leave it in the kettle for no more than 30 minutes. This keeps it at 70°C or above, which is hot enough to deal with germs in the powder.
A filter does not replace this step. Filtered water can sit in a tank and in pipes before it reaches your glass. So boil it, just as you would with tap water.
The HSE also notes that some formula machines may not heat water to 70°C. If you use one, check this carefully.
Once the bottle is made, cool it under cold running water. Test a drop on your inner wrist. It should feel lukewarm. Throw away any milk left after two hours.
What about boil water notices and private wells?
If your area has a boil water notice, follow the advice from Uisce Éireann and the HSE in full. Having a home filter is not a reason to skip it.
If your home uses a private well, the picture is different. Wells are not covered by the public supply figures above. Please have your well water tested before using it for baby feeds. Your local authority can advise you on how to do this.
How do I keep RO water safe day to day?
A few simple habits make a real difference.
Change your filters on the schedule your supplier gives you. A filter past its best will not work as it should. Keep your bottles and teats clean and sterilised. Use fresh water from the tap each time you boil the kettle.
If your baby is under six months and fully formula fed, they usually get all the fluid they need from their feeds. Your public health nurse can guide you on when to offer water on its own.
What would I suggest for families who want peace of mind?
If you would like cleaner water at your kitchen tap, a reverse osmosis system is a practical choice. The ArkkZ Water Filtration System from Renewell Water gives you RO water for drinking and for making up feeds.
Renewell Water is Ireland's Number 1 rated water filtration company, and you can read what families say in their customer reviews.
Renewell Water offers a free consultation for you. Book it by clicking here.
This article is for general information only and is not medical advice. Every baby is different. If you have any questions about feeding your baby, or if a concern persists, please speak to your GP or public health nurse.