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Base de datos de evaluación

Evaluation report

VTN 1998/019: Study on the Possible Pollution Caused by Water Seal Latrine to Ground Soil and Water After 10 Years of Operation

Author: Centre of Environmental Chemistry (CEC), University of Science, Hanoi National University

Executive summary


Since 1986, pour flush water seal latrine (WSL), a type of pit latrine, has been introduced in Vietnam by the Ministry of Health and UNICEF. Though the results of the preliminary assessments of the constructed water seal latrines after six months, one year and two years did not show any signs of contamination at the surrounding water sources and unsuitability of the utilization of pit latrine, the question arises as to whether the water seal latrine is the source of the contamination from on-site sanitation after long-time operation, and practically still need to be solved. At the request of UNICEF and the Ministry of Health, an investigation project named "Study on the possible pollution caused by water seal latrine to soil and groundwater after 10 years of utilization" was conducted by the Centre of Environmental Chemistry, University of Science, Hanoi National University from July to Nov. of 1999.

Purpose / Objective

The principal concern was whether the contamination of microorganism from water seal latrine on surrounding soil and groundwater occurred or not. Of less immediate concern, but potentially a more persistent problem, is the chemical contamination of groundwater by organic, phosphorus, nitrogen compounds that are evaluated via parameters BOD5, nitrate, nitrite, and ammonia.

The specific objectives of the study are to:
- Find out whether seepage from constructed latrines produces contamination of soil and groundwater or not
- Assess the possibility of chemical contamination derived from latrine effluent to groundwater
- Assess the durability and effectiveness of the constructed latrines


Nghia Do and Tan Truong communes where water seal latrines were built in 1988-1990 under the UNICEF-assisted project was selected for this study. 24 water seal latrines built from 1989 to 1992 were selected in the two communes, for investigation of the durability and sanitation after ten years of operation. 16 out of them were subjected for evaluation of possibility of causing contamination on surrounding soil and groundwater. The data set comprises 124 groundwater samples and 260 soil samples taken at different distances and depths over two periods of studies that are representative for rainy and dry seasons. The analyses were done for BOD5, DO, NO3-, NO2-, NH4+, PO43-, pH, to, and fecal coliform. Only fecal coliform is determined for soil contamination evaluation.

Key Findings and Conclusions

The contamination caused by water seal latrine on surrounding soil and groundwater was not found in this period of study. In addition, comparing with the data collected by a study conducted in 1989-1990, there was no evidence of accumulated bio-chemical pollution caused by the water seal latrines to soil and groundwater after ten years of operation. The absence of fecal coliform at the distance of 8m from latrine to the surrounding environment has shown that this distance is safe enough for the loamy soil condition, especially of the Red River Delta. Chemical groundwater quality showed that 50 wells met WHO and Vietnamese standard and was not affected by effluent from latrines.

The physical conditions of the water seal latrine (only 25% and 16.7% among 24 latrines appearing their damage with small cracks on the walls and root) and its cleanness showed that the latrine is durable and accepted by the users.


A number of water seal latrines constructed in the past were found converted into septic tank latrines. This shows a real sanitation evolution in the countryside. However, in the present economic context, this step is not economically sound. It would have been better if the conversion was made for the dry latrines being widely used in the communes.

It is recommended that more emphasis should be given to sanitation and hygiene motivation, facilities and education to maximize the potential benefits of water supply. A good water supply system would bring no changes to the people's health unless the users are well-educated on how to use and maintain it properly.

Fecal coliform was found in almost soil samples at the depth of 0.4m and 1m, even in reference samples after heavy rains. This would be a reason of bacteriological contamination of shallow groundwater by the percolation. Therefore, investigating the pathway of contamination from surface pollution sources to ground water should be paid greater attention.

As some of the water seal latrines were found too close to the water source and surrounding pollution source, it is recommended that a safe distance of a minimum 8m should be kept and monitored by the health sector at the grassroots level.

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Report information





Water and Environmental Sanitation

Vietnam Ministry of Health


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