Germs in drinking water: why bacteria, parasites and viruses matter most in pregnancy and for babies

Unlike the other contaminants on our list, germs in water make people ill in days, not years, and pregnant women and young children are hit hardest. What the main culprits do, how each one is stopped, and what a family can do.

Every other contaminant on our homepage works slowly, over years. Germs in water — bacteria, parasites and viruses — work in days, sometimes hours, and some of them need only small amounts of water to make someone ill. Worldwide, the World Health Organization estimates that contaminated drinking water causes around 505,000 deaths from diarrhoea every year. It is the oldest danger in drinking water, and still the biggest.

Where water is treated properly it is also the best controlled, which is exactly why it is easy to forget. When something goes wrong — a broken main, a flood, an old storage tank, a well nobody tests — the people who suffer first and most are pregnant women, babies and young children.

Why pregnancy and early childhood are most at risk

Pregnancy changes the immune system. To protect the baby, part of the mother’s immune defence is turned down, and some infections become more serious. The best-known example, Listeria, comes mostly from food rather than water, but it shows the pattern: pregnant women are about ten times more likely than other adults to get it, and it can cause miscarriage, stillbirth or premature labour.
Small children dehydrate fast. A young child has less fluid in reserve, and a bout of diarrhoea that an adult shrugs off can leave a toddler dangerously dehydrated within a day. Repeated bouts also get in the way of growth, because the gut stops absorbing food properly.

Bacteria: E. coli, Salmonella, Campylobacter

How they get in. From human or animal waste: sewage overflows, failing septic tanks, manure washed into a well by heavy rain.
In children. Some strains of E. coli, O157 among them, make a toxin that can cause haemolytic uraemic syndrome (HUS), which damages the kidneys. Between 5 and 15 per cent of children infected with these strains develop it, most often under the age of five, and it is the commonest cause of sudden kidney failure in young children.
In pregnancy. A serious infection with a high fever is a risk in pregnancy in its own right and needs a doctor promptly.
What stops them. Proper chlorination kills them. In Walkerton, Canada, in 2000, cattle manure washed into a town well after heavy rain and the treatment failed: more than 2,000 people fell ill with E. coli O157 and Campylobacter, and seven died.

Parasites: Cryptosporidium and Giardia

How they get in. Also from human and animal waste, and they are built to last: Cryptosporidium’s tough outer shell lets it survive the chlorine that kills bacteria, and Giardia is harder to kill with chlorine too.
What they do. Watery diarrhoea that can go on for one to several weeks, with the dehydration that brings for a pregnant woman or a small child. In Milwaukee in 1993, Cryptosporidium got through the city’s water treatment and an estimated 403,000 people fell ill, the largest waterborne outbreak recorded in the United States.
What stops them. Boiling, a filter certified to NSF/ANSI 53 or 58 for “cyst reduction”, reverse osmosis, or ultraviolet light.

Viruses: norovirus, rotavirus, hepatitis A and E

How they get in. They are shed in human faeces and reach water through sewage, and through wells and systems where treatment is poor or missing.
Rotavirus was the leading cause of severe diarrhoea in babies and toddlers before vaccination; in the United States alone it put 55,000 to 70,000 children in hospital every year. It spreads mostly from person to person and sometimes through water, and a vaccine given as drops in the first months of life now prevents most of those hospital stays.
Hepatitis E is the one to know about in pregnancy. It is uncommon in Europe and the United States and mostly a disease of places without safe water and sanitation, but there it is severe: up to 20 to 25 per cent of women infected in the third trimester can die, from liver failure.
What stops them. Proper chlorination, ultraviolet light, or boiling.

At a glance

Germs	Examples	What stops them	Main risk in pregnancy and early childhood
Bacteria	E. coli, Salmonella, Campylobacter	Proper chlorination, ultraviolet light, boiling	Kidney damage from HUS in young children; serious infection in pregnancy
Parasites	Cryptosporidium, Giardia	A filter certified for cysts, ultraviolet light, boiling — chlorine alone is not enough	Weeks of diarrhoea and dehydration
Viruses	Norovirus, rotavirus, hepatitis A and E	Proper chlorination, ultraviolet light, boiling	Rapid dehydration in small children; hepatitis E dangerous in late pregnancy

What you can do

Against germs, unlike against metals, boiling works — which makes this the one contaminant a family can deal with on its own stove when it has to.

Follow boil-water notices to the letter. Bring the water to a rolling boil for one minute (three minutes at high altitude), and use it for drinking, cooking, brushing teeth and making formula.
Test a private well at least once a year for bacteria, and again after a flood or any change in its taste, smell or colour.
Look after stored water. Roof tanks and cisterns that are never opened or cleaned are a common way for clean water to become unsafe on its last few metres.
For extra protection at the tap, choose ultraviolet disinfection, a filter certified for cyst reduction under NSF/ANSI 53 or 58, or reverse osmosis, and keep it serviced.
Make formula with water you know is safe, boiled or from a supply you trust, and wash your hands before preparing it.
Vaccinate against rotavirus, as paediatricians recommend.

Why this matters to us

This is the risk the Foundation’s work began with. The children’s homes and shelters we serve in Greece, and the organisations for pregnant women and young mothers we are working with in New York and New Jersey, cannot afford a single bad week of water.

That is why the Twin system that our partner NearonYdor fits in the homes we fund in Greece was tested by the Hellenic Pasteur Institute, working to European Pharmacopoeia methods under ESYD accreditation: water carrying over 300 colony-forming units of bacteria per millilitre came out at zero. And it is why we pay for the servicing as well as the equipment, because a filter nobody maintains stops protecting anyone.

If you would like to help us bring the same water to more mothers and children, the ways to give are on our donate page.

Sources

World Health Organization, Drinking-water, fact sheet (2023).
Centers for Disease Control and Prevention, Clinical overview of listeriosis.
Colorado Department of Public Health and Environment, Hemolytic uremic syndrome (HUS).
Drinking water contamination in Walkerton, Ontario: positive resolutions from a tragic event (2003).
Corso et al., Costs of illness in the 1993 waterborne Cryptosporidium outbreak, Milwaukee, Wisconsin, Emerging Infectious Diseases (2003).
Centers for Disease Control and Prevention, Preventing Crypto at home during a boil water advisory and How to make water safe in an emergency.
World Health Organization, Hepatitis E, fact sheet.
Centers for Disease Control and Prevention, Sustained decrease in laboratory detection of rotavirus after routine vaccination, United States (2015), and Rotavirus vaccination.
Centers for Disease Control and Prevention, Guidelines for testing well water.
Laboratory report, Hellenic Pasteur Institute (ESYD accreditation no. 516-5).