Abstract: Tooth decay or caries is the most common disease found in oral cavity. Caries experience of children aged 12 years or older in South Kalimantan reached 83.4% thus placing the disease as the main problem of oral health. According to 2013 Riskesdas/basic health research, the highest tooth decay index in South Kalimantan was found at Barito Kuala (48.6%) and Banjarmasin (23.8%), the numbers were higher than province’s average of 36.1% with DMF-T index of Barito Kuala, Banjarmasin and South Kalimantan as high as 6.61, 5.54 and 6.83, respectively. Both of the regions had river water flowing through them which were streaming in from the swamps around the river area or commonly known as wetland or peat. The condition eventually produced water with pH around 3.5-4.5. The community’s dependence on that water for consumption and in particular, their incorrect teeth brushing technique greatly affected tooth decay. Data shown pointed out percentage of the correct teeth brushing technique only reached 3.4, 11.3, 5.0% for Barito Kuala, Banjarmasin and South Kalimantan, respectively. DMF-T index counting at Madrasah Tsanawiyah and chosen high schools in both regions on June 2014 showed numbers of DMF-T in community using PDAM water for teeth brushing as 2.05, river water as 5.46 with DMF-T average of 3.75 (moderate). The life style of teeth brushing using river water aggravated tooth decay progress. Empowerment of community by civilizing people to use water qualifying in adequate health requirements could be utilized as a preventive effort to decrease caries index.