Adding fluoride to water can improve the dental health of the nation's children, a new report suggests.
Youngsters living in areas where water fluoridation schemes are in place are less likely to have tooth decay than those in other regions, according to a Public Health England (PHE) report.
Experts said there are "significant benefits" of the schemes after compiling the first national report on the measure.
During the early 20th century lower levels of tooth decay were noted in places which had certain fluoride levels in drinking water.
Over the last 50 years, schemes have been put in place in various places across England to adjust the levels of the mineral in water supplies to mimic the effect.
In England, 14 out of 152 local authorities have water fluoridation schemes in place - covering six million people.
In these areas the level of fluoride in the water is adjusted to one part per million. In the latest report, experts measured the dental health of five-year-olds with baby teeth and 12-year-olds with adult teeth from fluoridated and non-fluoridated areas.
On average, 15% fewer five-year-olds have tooth decay that needed intervention in fluoridated areas, the authors said.
And when deprivation and ethnicity - both important factors for dental health - are taken into account this figure rises to 28% fewer cases of tooth decay.
Meanwhile there are 11% fewer 12-year-olds with tooth decay in fluoridated areas compared to non-fluoridated areas.
This figure rose to 21% when deprivation and ethnicity were taken into account, the authors said.
And in areas which participate in the water adjustment scheme there are 45% fewer hospital admissions for tooth decay among children aged one to four.
Experts also found that the population rates of kidney stones and bladder cancer were lower in fluoridated areas.
While the findings are only a crude analysis, the authors found that kidney stones episodes were 5.3% lower in fluoridated areas and rates of bladder cancer were 4.4% lower in fluoridated areas compared to non-fluoridated places.
But they said more research was needed to assess these findings.
A previous study has linked fluoridation to dental fluorosis - where white flecks are seen on the teeth.
The research compared rates of the effect on fluoridated Newcastle and non-fluoridated Manchester.
They found that the number of 12 year old children in Newcastle with moderate dental fluorosis was around 1% compared to 0.2% in Manchester.
But the authors said the overall dental benefit of the schemes were "important".
"Dental caries (tooth decay) is a significant public health problem in England," the report states.
"Sizeable inequalities in the incidence of caries exist between affluent and deprived communities, and it is a common cause of hospital admissions in children."
Professor John Newton, chief knowledge officer at PHE, said: "There is a good deal of speculation about water fluoridation schemes. This report provides new data which is direct evidence of the safety and efficacy of water fluoridation in England.
"There is no evidence of any effect on general health in fluoridated areas compared to non-fluoridated areas. There are important benefits in terms of dental health - it does look as if there are really significant benefits in those areas that have water fluoridation schemes.
"We will use this report as a basis for discussions with local authorities on the scope and content of further reports and on the role of fluoridation as a public health measure."
Sue Gregory, director of dental public health at PHE, added: "These findings highlight the important contribution that water fluoridation makes to children's dental health and general well-being.
"It is notable that the benefits of this public health measure appear to be greatest for children living in the most deprived areas of the country.
"This is significant for reducing the large differences we see in dental health between deprived and more affluent areas of the country."