Water quality is the first consideration in choosing water resources for many purposes, especially for drinking and
irrigation. In the Mekong Delta, the quality of water resources deteriorated severely by variable pollutant sources such as
wastewater, arsenic and seawater. This paper aims to assess water quality for domestic and irrigation uses in coastal
areas of Soc Trang province, the Mekong Delta, Vietnam. The water quality index (WQI) and variable irrigation water
quality indexes (IWQIs) such as sodium adsorption ratio ( SAR), Kelly's ratio (KR), residual sodium carbonate (RSC),
solute sodium percentage (SSP) and permeability index (PI) were deployed to evaluate water quality regarding domestic
and agricultural water demands. Water samples were taken by seasonal characteristics and tidal regime in 2013 and 2014.
Main parameters include Temperature (T0C), Electrical Conductivity(EC), pH, Dissolved Oxygen(DO), Total Dissolved
Solid (TDS), Total Hardness (TH), calcium (Ca2+), magnesium (Mg2+), sodium (Na+), bicarbonate (HCO3-), chloride (Cl-
),
sulfate (SO42-) and nitrate (NO3-) were analyzed for the calculation of WQI and IWQIs. The results show that, almost
groundwater samples at shallow aquifers, some of the deeper aquifers and river water samples in dry season were
seriously affected by seawater intrusion and nitrate contamination. This means that these water resources cannot use for
both drinking and agricultural purposes. Meanwhile, most of groundwater samples at middle and lower Pleistocene
aquifers and surface water in rainy season seem to be good for both drinking and irrigation. However, groundwater
source in Soc Trang province has been excessively extracted without suitable regulation and appropriate management.
This situation may threat to groundwater source because it can be easily contaminated by seawater intrusion and
wastewater. In order to extract, use and manage effectively fresh water source in coastal areas in the Mekong delta,
emergent management practices should be considered.