Source-water salinity measured by electrical conductivity in Bangladesh, 2025: a nationally representative cross-sectional survey
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Background
In coastal Bangladesh, salty drinking water has been linked to higher blood pressure, including in pregnancy. Bangladesh has no national estimate of how many people use salty water sources. The 2025 Multiple Indicator Cluster Survey measured electrical conductivity, a marker of salinity, in household water sources. However, its report gave no counts of people affected, no district results and no link with arsenic.
Objectives
To estimate how many people live in households whose tested water source has high salinity, and where they live. A further aim was to describe how high salinity varies by household characteristics and source type, especially deep against shallow tube wells, and whether it occurs together with arsenic.
Methods
Electrical conductivity was measured in the water source of 6,040 households in all 64 districts, from February to June 2025. In 14.5% of households, the tested source was not the main drinking-water source. The main outcomes were conductivity above 1,500 and above 3,000 µS/cm, which are the survey’s risk classes, not health-based standards. All estimates used the survey weights and design. Deep and shallow tube wells were compared with models adjusted for place, elevation, rainfall, residence and wealth.
Results
The tested source exceeded 1,500 µS/cm in 5.3% of households (95% confidence interval 4.7 to 5.9). About 9.0 million people (7.9 to 10.1 million) lived in these households, including 1.8 million whose source exceeded 3,000 µS/cm. The 19 coastal districts held 26% of households but 70% of those above 1,500 µS/cm. In these districts, 14.1% of households were above this level, against 2.1% elsewhere. Estimates for all 64 districts are provided. Prevalence was similar across wealth quintiles and in households with a child under 5 or a pregnant woman. Nationally, deep tube wells had high conductivity more often than shallow wells (11.9% against 4.2%), mainly because most deep wells are in the coastal zone. Within the coastal zone, the shares were similar (16.1% against 17.9%). After adjustment for district, conductivity in deep wells was about 18% lower (geometric mean ratio 0.82, 0.73 to 0.92). Within subdistricts, using a smaller sample, the ratio was 0.93 (0.80 to 1.07). Arsenic above 10 µg/L was more common where conductivity was high, but this link weakened after adjustment for district. About 2.2 million people lived in households whose source exceeded both 1,500 µS/cm and 10 µg/L arsenic.
Conclusions
Millions of people in Bangladesh live in households whose water source is highly saline, mostly in coastal and south-central districts. Deep wells were somewhat less saline than shallow wells in the same district, but the difference shrank within subdistricts and depended on how very low readings were handled. A source that is safe for arsenic is not necessarily low in salt. National water surveys should measure salinity alongside arsenic, record how meters are calibrated, and test water in more than one season.
