The increasing environmental pressures associated with cement production and industrial waste disposal have highlighted the urgent need for sustainable alternatives in construction materials. However, despite the growing interest in waste-derived binders and alternative mixing waters, the combined use of ceramic waste and untreated coal washed wastewater (CWW) in structural reinforced concrete elements remains largely unexplored. In particular, there is a lack of scientific understanding regarding how these two distinct waste streams jointly influence flexural behaviour, crack development, stiffness evolution, and microstructural characteristics in loadbearing members. This study addresses this gap by investigating the structural and microstructural performance of reinforced concrete beams produced by partially substituting Portland cement with ceramic waste and replacing conventional mixing water with untreated CWW. Ceramic waste was alkali-activated using sodium hydroxide to enhance its pozzolanic reactivity, while CWW-rich in fine coal particles and dissolved minerals-was incorporated without pre-treatment. Three beam series were prepared: a control mix, a mix with 50 % cement replaced by ceramic waste, and a third mix combining ceramic waste substitution with full replacement of clean water by CWW. Three-point bending tests evaluated flexural capacity, stiffness degradation, ductility, energy absorption, and crack propagation. The results revealed that although ceramic waste and CWW caused a modest (similar to 9 %) reduction in compressive strength, the decrease in flexural performance was smaller (5.9 %). The modified beams exhibited similar crack initiation patterns, narrower crack widths, and enhanced post-cracking ductility. Microstructural analyses (XRD, FTIR, SEM-EDS) confirmed the formation of calcium-alumina-silicate-hydrate (C-A-S-H) phases in ceramic waste mixes, while CWW did not hinder hydration mechanisms. Overall, the findings demonstrate that the combined use of ceramic waste and CWW yields structurally reliable and environmentally favourable concrete elements. This work therefore not only provides a practical pathway for valorising two major industrial by-products, but also fills a significant scientific gap by clarifying their coupled effects on the flexural and microstructural behaviour of reinforced concrete beams.