This study aims to investigate the impact of groundwater containing composite salts on the compressive strength of concrete foundations located in the city of Basra in Iraq. The groundwater in this city demonstrates high concentrations of salts, particularly significant amounts of magnesium, sodium, and calcium salts, which are present in close proximity to the soil surface. To accomplish this objective, a foundation in the mentioned city was selected, which has been constructed since 2012 and remains incomplete to this day. The chosen foundation covers an area of approximately 2000 m2. Samples were collected from seven distinct regions, with three samples obtained from each region, resulting in a total of 21 samples. The selected regions were those most affected by groundwater, specifically those closest to the soil, such as regions near edges or openings within the foundation. The results of compressive strength tests conducted on all specimens indicated a remarkable decline in compressive strength. On average, the findings revealed a 30% reduction in compressive strength, highlighting the significant impact of composite salt-contaminated groundwater on the durability of concrete foundations.