Lao PDR - Estimating the fluoride concentration in the drinking waters

by GL. Tayanin*, Faculty of Odontology, Malmö University, Sweden

The concentration of fluoride in drinking waters is one of the factors strongly influencing the dental caries situation globally. Data on fluoride sources in Lao People's Democratic Republic is only available to a limited extent (1). The aim of this study was to collect drinking water samples from some different parts of Laos using a standardised method for fluoride determination and eventual pilot fluoride mapping of some provinces of the country. This information would be very useful in the planning and implementation of oral health primary prevention programmes in the future.

Materials and Method
Drinking water samples were collected from different parts of the country in July 1999.

Sample Collection:

Samples were collected from 50 different samples of drinking water, representing big and small cities and villages. Drinking water from each source (see below) such as bottled, tap, hand pump, springs, stream, lake and rivers were collected in clean and dry 60 ml polypropylene containers. Each sample was labelled giving the time, date, site and source. When collecting tap water, the tap was allowed to run for a few minutes so as to collect an evenly distributed sample of water.

The starting point of the water sample collection was the capital Vientaine which belongs to the Vientaine Municipality. Water samples were collected from tap, bottled water, ice cubes and the river (Table 1). From here moving north, samples were collected from the Vientaine Province, then from the mountainous province of Xiengkhouang (2000 m above sea level), then going northwestwards from Luang Prabang province (500-1000 m above sea level) and Oudomxay province (1000 m above sea level) and returning to the capital. 

The samples were analysed for fluoride concentration using standard methods in the Department of Cariology, Faculty of Dental Sciences, University of Malmö Sweden.

Analysis of fluoride in water samples:

After collection the samples were stored in a refrigerator. The F- concentration was analysed two weeks later by using an ion-specific electrode and difference electrode, Fluoride Electrode Instrument (Orion).

  • Prepared standard solution ranging between 1.0 ppm - 0.1 ppm were chosen presuming that the unknown sample concentration of fluoride may fall in between these two standards.
  • TISAB (Total Ionic Strength Adjustment Buffer), was added to the standard fluoride solutions to adjust the pH of the sample and to break up complexes.
  • The instrument was calibrated with the two standard solution.
  • To each water sample TISAB III was added in correct ratio.
  • To determine the F- concentration, the electrode was left to stand in the solution for 3 minutes.
  • After 3 minutes the F- concentration in the water sample was read directly from the digital display meter.

For each sample, two fluoride readings were taken. 43 (86%) of the 50 samples showed no difference between the two measurements. 0.01 difference was seen in 3 (6%) of the samples, 0.02 and 0.03 differences were observed in 1 (2%) and 3 (6%) samples respectively. Only the first reading was included in the study.

The main drinking water source is the Mekong river in Vientiane municipality. Usually water is boiled before drinking in Laos. Highest concentration of fluoride was recorded in the Luang Prabang province, in the water sample from a hand pump which was 0.512 F- ppm. The lowest level of 0.013 F- ppm was observed from a stream in the Nakanthung village, Vientiane province, and from bottled water in Moung Xay district in Oudomxay province.

Fluoride concentrations (ppm) in various water sources in different provinces in Laos, July 1999

Province: Vientiane Municipality

District/Place Type of Source No. of samples F- conc. range (PPM) F- conc. mean (ppm)

Vientiane Mun./Mekong R


River - 0.101

Chanthabury/Saylom Vil


Tap 1 - 0.089

Chanthabury/Nam pu Square

Tap 3 - 0.114

Chanthabury/Mahosot Hosp

Tap 1 - 0.111


Bottled 1 - 0.123


Ice Cubes 1 0.038-0.039 0.039

Sisattanak/Dongpalan Vil

Tap 1 0.099-0.110 0.105


Sapanthongneau Vil

Tap 1 0.100-0.117 0.109


Bottled 1 0.105-0.140 0.118


Province: Vientiane

District/Place Type of Source No. of samples F- conc. range (PPM) F- conc. mean (ppm)
Saythany/NongbuaVil Lake 1 - 0.015
Saythany/Nakanthung Vil


1 - 0.013
Saythany/Prabadaewkhan Vil Water fall 3 0.010-0.011 0.010
Saythany Bottled 1 - 0.096
Phonesavanh Vil/Nam Ngum Tap 1 - 0.034
Sikhottabong/Wat Tay Vil Tap 1 - 0.105
Vang Vieng/Nam Song R. River 1 - 0.031
Vang Vieng Spring 1 - 0.034
Vang Vieng Tap 1 - 0.033

Province: Xiengkhouang

District/Place Type of Source No. of samples F- conc. range (PPM) F- conc. mean (ppm)
Phonesavanh Tap 3 0.053-0.058 0.056
Phonesavanh Bottled 2 0.052-0.062 0.057
Phonesavanh Hand-pump 1 - 0.022


Province: Luang Prabang

District/Place Type of Source No. of samples F- conc. range (PPM) F- conc. mean (ppm)
Luang Prabang/Mekong R.  River  2 0.082-0.083   0.083
Luang Prabang/Nam Ou R.  River  1  - 0.057 
Luang Prabang/Tad Khwangsi  Water fall  2  0.043-0.048  0.045 
Luang Prabang Tap 2 0.026-0.029  0.028
Luang Prabang Bottled 2 0.026-0.029  0.028
Luang Prabang Ice cuber 1 - 0.026
Luang Prabang/Lakpad Vil Handpump 1 -  0.512
Luang Prabang/Soub Kong Vil Tap 1 - 0.084
Moung Ngoi Tap 1 - 0.127


Province: Oudomxay

District/Place Type of Source No. of samples F- conc. range (PPM) F- conc. mean (ppm)
Moung Xay Spring 1 - 0.041
Moung Xay Tap 3 0.014-0.052 0.036
Moung Xay Bottled 1 - 0.013


Fluoride Map : showing the fluoride concentrations observed in the water samples taken from some provinces in Laos.

The WHO in 1994 has recommended fluoride levels of 0.5-1.0 mg/l (0.5-1.0 F- ppm) in the drinking water for optimal cariostatic effect, the lower limits for hot climate (as people drink more water) and upper limit for cold climates (2). The concentrations of fluorides in the drinking water observed in this study are below this optimal level. The study tells that one important factor contributing to caries resistance is missing. Should caries-inducing factors increase in Laos, for example the consumption of sucrose and other caries inducing carbohydrates, the need for effective oral health primary preventive programmes is great, greater than if fluoride had been present.

Wong Hee Deong, Implementation of the oral health component of the health-promoting school project, mission report, WPRO/WHO, 1997.
Fluorides and oral health, report of a WHO Expert Committee on Oral Health Status and Fluoride Use, 1994, WHO/Geneva.

Thanks are due to Dr Khamhoung Prommavongsa, Chief of Dental Service, Mahosot Hospital, Vientiane, for valuable discussions on the oral health situation in Laos.

We also wish to thank profusely Dr Somphone Doangchannalad, Chief of Dental Service, Luang Prabang, Dr Sinsay, Chief of Dental Service Xiengkhouang, Mr Norm Chief of Dental Service, Oudomxay, for their generous and enthusiastic contribuions which enabled us to gain insight on practising dentistry in Laos.

* This project was performed by GL. Tayanin as a Student Research Project at the Faculty of Odontology, Malmö University, Sweden under the guidance of Prof. D. Bratthall and Dr JR. Stjernswärd. Mrs E. Thornqvist was supervising the fluorie determinations in the laboratory.

Water sources

...Water tap standing in the center of Soubkong village, Luang Prabang, providing water to the villagers

.. Bottled water - Vientiane ..

.. Bottled water - in a big bottle - Xiengkhouang ..

...Children pumping water at Lakpad village, Luang Prabang

.. Cool ..

...Clear water from the handpump..which is provided for all the villagers

...Another handpump at a hillfoot of the Plaine of Jars, Xiengkhouang

...Running water from a bamboo tube, on the way to Oudomxay

.. Nongbua Lake, Vientiane ..

.. Ou River, Luang Prabang ..

.. Kwangsi Waterfall, Luang Prabang ..

.. Kwangsi Waterfall, Luang Prabang ..

..all photos by D. Tayanin

Water sample collection

...When collecting tap water, water was allowed to run for a few minutes and then collected in the clean 60 ml plastic bottle. Here collecting water from a tap inside a house.

...from a hand pump, which provides water for people at a foot of the Plain of Jars hill, Xiengkhouang

...from a stream, Vientiane

...from a spring which is being directed through open bamboo tube. This spring water is provided on the way to Oudomxay

... from Kwangsi waterfall, Luang Prabang

Province: Vientiane

.. Friendships bridge across Mekong River - 
connecting Laos and Thailand ..

.. Thadeua - Vientiane, taken from Thai-side ..

.. That Luang..

.. Inside Vientiane..

.. How much? ..

.. Bambooshoots ..

.. Transportation across Song River..

.. Shall we..? ..

.. Late afternoon - children enjoy bathing ..

.. Children at the stream ..

.. Cool ..

.. Brr..(??) ..

.. Return from paddy ..

.. Kwao Tung - Vangvieng ..

.. At the Ngum River bank ..

All photos by: Damrong Tayanin

Province: Xiengkhouang

.. At the Plaine of Jars ..

.. Rocky Jars..

.. On the hill ..

.. Cloudy ..

.. up to the hill ..

.. On the way ..

All photos by: Damrong Tayanin

Province: Luang Prabang

.. Inside Luang Prabang ..

.. Ou River ..

.. Kwangsi waterfall ..

.. Temple bells, Muang Ngoi ..

.. Amm..dinner at the courtyard

..Fishing boat..

All photos by: Damrong Tayanin

Province: Oudomxay

.. Viewing over the town ..

.. Pagoda standing on the hill ..

.. Four wheels waiting at the foot of the hill ..

.. Kammu village situated on the mountain slope ..

.. Kammu village ..

.. Kammu girl carry the younger one on her back ..

.. A Hmong - on the mountain ..

.. ZZZ ..

All photos by: Damrong Tayanin