Making children drink tap water protects them against tooth decay, according to new research.
But it can lead to blood poisoning if the water is contaminated with lead, warn scientists.
The study found blood lead levels lower but tooth decay higher in children who drink bottled rather than tap water. The latter contains teeth boosting fluoride.
The findings published in the American Journal of Preventive Medicine in September 2017, show there is a trade-off for parents to weigh up.
Dr Anne Sanders, of the Department of Dental Ecology at the University of North Carolina at Chapel Hill, said: "Elevated blood lead levels affect only a small minority of children, but the health consequences are profound and permanent.
"On the other hand, tooth decay affects one in every two children, and its consequences, such as toothache, are immediate and costly to treat."
In the US there has been a huge surge in cases of lead poisoning in the last three years, particularly in Flint, Michigan, where the entire water supply was contaminated. after the drinking source was changed to the untreated Flint River.
A federal state of emergency was declared and residents were instructed to use only bottled or filtered water for drinking, cooking, cleaning and bathing.
Even before the crisis, there was public mistrust of tap water safety. But avoiding fluoridated tap water raises another public health concern - children are denied its protection from tooth decay.
According to the Centres for Disease Control and Prevention (CDC), adding fluoride to the water supply has dramatically reduced the prevalence of tooth decay over the past 70 years.
But tooth decay remains widespread. In 2011-2012, it affected the primary teeth of 23% of under fives.
The number of British children aged four and under being hospitalised for tooth extractions has risen by almost a quarter in the last decade, new figures have revealed.
There were 9,206 extractions among this age group in 2015/16 - up from 7,444 in 2006/7, according to data obtained by the Faculty of Dental Surgery at the Royal College of Surgeons (RCS).
Dr Anne Sanders and co author Dr Gary Slade analysed almost 16,000 two to 19 year olds across the US who participated in the National Health and Nutrition Examination Survey (NHANES) from 2005 to 2014.
More than 12,000 records included data on blood lead level and about 5,600 had tooth decay examination data.
Following an in-home interview, participants visited a mobile examination centre where they donated a blood sample, completed a dietary interview and received a dental examination.
About one in seven (15%) stated they did not drink tap water. An elevated blood lead level was defined as having at least three micrograms of per deciliter of blood.
Those who drank tap water had significantly higher blood lead levels. Overall, it affected nearly 3% compared to half (49.8%) who had tooth decay.
Dentists say 90 per cent of tooth decay is preventable through reducing sugar consumption, regular brushing with fluoride toothpaste and routine dental visits.
In the UK, 42 per cent of children did not see a dentist in 2015/16, despite NHS dental treatment being free for under 18s.
Tooth extraction is the number one reason for the hospitalisation of children aged five to nine, according to NHS Digital.
From April 2018, soft drinks will see a tax hike of 24p per litre for the most sugar-filled drinks and 18p per litre for drinks with more than five but less than eight grams of
sugar per 100ml.
Flint, Michigan, has been the poster child for water contamination since the issue arose in 2014. Lead seeped into the water and nearly 8,000 children are believed to have been exposed to lead poisoning.
Lead exposure is particularly dangerous for infants and young children. It can cause serious long term health problems.