The popularity of bottled water may be bad news for kids’ teeth.

Australian researchers found that children who drank bottled water and other unfluoridated water had an increased risk of decay in their baby (primary) teeth, compared with children who drank only fluoridated water.

The study did not find an increased risk of decay in permanent teeth.

Nearly 10,000 children participated in the research. The researchers collected information on how often each child drank water from a private source (either bottled water, or water from tanks that collect and filter rainwater), compared with public, fluoridated water.

Forty-five percent of the children got more than half of their water from the unfluoridated sources; 36 percent never drank unfluoridated water. Children from non-urban areas, children from two-parent families, and children from lower socioeconomic groups were more likely to drink bottled water or water from rainwater tanks.

In the United States, not all public water sources are fluoridated, but many are. Children who live in homes with unfluoridated water are encouraged to take fluoride supplements, which can be prescribed by a dentist. Most bottled water in the United States is not advertised as fluoridated, though some may contain it. For example, about 5 percent of bottled water sampled in an Ohio study was found to contain state-recommended levels of fluoride.

The Australian study appears in the August issue of Community Dentistry and Oral Epidemiology.