Groundwater is an important source of water in Sharjah, which is located in one of the most water-stressed regions in the world. Therefore, efficient management is essential to sustain groundwater resources in Sharjah. In this study, spatial and temporal trends in monthly groundwater quality data, which were received from eleven well fields in Sharjah over the period of 1985–2017, were reported. The Mann-Kendall and Sen’s slope estimator tests were adopted as non-parametric trend tests for temporal (trend) analysis, whereas penalized Splines (P-Splines) was used in spatial trend analysis. Statistically significant increasing trends with high Sen’s slopes were detected in chloride, electrical conductivity and total dissolved solids (salinity ions), indicating increasing salinity trends. Nitrate and nitrite parameters showed decreasing trends and were within the allowable limits for all well fields according to local Water Quality Regulations. Spatial maps showed the highest salinity, to be in the well fields closest to the coastal region, whereas the lowest salinity values were found in the well fields that are the farthest from the coastal region. This study is expected to provide beneficial input for groundwater policymakers and managers in Sharjah for sustainable groundwater management.