Aim of the study:
Although groundwater is a primary source of accessible freshwater, it is also particularly susceptible to contamination. Recognizing its importance is crucial for ensuring clean and sustainable drinking water on a global scale. The Thrace Region, renowned for its fertile agricultural lands, faces environmental pressures as agricultural and livestock activities pose a potential risk to local freshwater quality. This study aimed to assess the seasonal variation in drinking water quality in the Lalapaşa district of the Edirne province, within the Thrace Region, by analysing a range of physicochemical parameters.

Material and methods:
A total of 28 drinking water samples were collected from various villages in Lalapaşa during the summer, autumn, and winter seasons of 2020–2021. Each sample was analysed for the following twelve parameters: dissolved oxygen (DO), oxygen saturation (O₂%), pH, electrical conductivity (EC), total dissolved solids (TDS), suspended solids (SS), salinity, turbidity, nitrate (NO₃⁻), nitrite (NO₂⁻), phosphate (PO₄³⁻), and sulfate (SO₄²⁻). The results were evaluated against national and international drinking water quality standards. Furthermore, ecological assessment was conducted using the water quality index (WQI), and statistical analyses were carried out using factor analysis (FA) and the pearson correlation index (PCI).

Results and conclusions:
FA revealed three major factors – ‘salinity factor,’ ‘agricultural factor,’ and ‘oxygen factor’ – which together explained 74% of the total variance. Despite elevated concentrations of nitrogen and phosphorus in some samples, WQI values at all stations remained within acceptable limits. These findings highlight the essential role of sustainable polyculture agricultural practices in protecting the region’s groundwater resources.