Rapid on-site detection of metals in water is essential for timely environmental assessment, especially in remote areas or time-critical situations. In this work, we present a portable measurement system that combines preconcentration filters with a portable X-ray fluorescence (pXRF) analyzer. Filters for Mn, Co, Ni, Cu, Zn, Pb, and U were fabricated using nanoporous silicon or silicon carbide with polymeric binders, while arsenic was captured using ferrihydrite-based filters. Water samples were collected from lakes, boreholes, and wells, and measured on-site. Detection limits as low as 12 µg/L for metals and 1.3 µg/L for arsenic were achieved, depending on sample volume. Results were validated against laboratory ICP-MS analysis. The lightweight, battery-operated setup enables field deployment with total measurement times as short as 15 minutes, offering a practical tool for preliminary screening and environmental monitoring in challenging conditions.