• As and hydrated silica elimination from deep well water by electrocoagulation (EC). • Aluminum sacrificial anodes in an EC reactor coupled to a flocculator-settler. • Aluminum and hydrated silica react, forming aluminosilicates, As adsorbs on flocs. • As concentration after EC treatment met the WHO guideline, hydrated silica is abated. • EC is a cheap (0.48 USD m −3 ) and accessible technology to treat natural groundwater. This paper shows the elimination of arsenic (As) and hydrated silica from natural groundwater (48.63 µg L −1 arsenic, 77.5 mg L −1 hydrated silica, 0.33 mg L −1 phosphate, 5 mg L −1 sulfate, 240 mg L −1 alkalinity, 89.5 mg L −1 hardness, pH 8.44 and 450 µS cm −1 conductivity) by electrocoagulation (EC). The flow plant employed a parallel plates EC reactor in series with a flocculator-settler. Aluminum was used as the sacrificial electrode. Before the electrolysis in the flow plant, a systematic study of the aluminum dose was carried using the EC reactor adapted to a jar test. The influence of the mean linear flow velocity (1.2–4.8 cm s −1 ) and current density (6–9 mA cm −2 ) on the removal of As and hydrated silica was addressed. The residual concentration of As and hydrated silica in the flow plant was C As = 4.2 µg L −1 and C hs = 4.5 mg L −1 , respectively, at 9 mA cm −2 and 1.2 cm s −1 , which agree well with that obtained in the jar test array. The residual As concentration fulfills the World Health Organization (WHO) recommendation (<10 μg L −1 ). The total operating cost of EC was 0.48 USD m −3 , considering electrolytic energy consumption, aluminum price, pumping costs, and sludge confinement. Flocs analyses performed by SEM-EDS, XRF-EDS, XRD, and FTIR showed the existence of aluminosilicates formed by the reaction of aluminum and hydrated silica. At the same time, As, phosphates and sulfates were separated by adsorption on flocs.