Water hyacinth (Eichhornia Crassipes) is one of the world’s most problematic invasive aquatic weeds, yet its rapid growth has a biomass productivity of 150-300 t/ha/year), high moisture content of 80-95%, volatile matter of 60-70% and mineral-rich composition also make it a promising, low-cost feedstock for biochar production. Published studies on water hyacinth-derived biochar remain fragmented across disciplines and are rarely synthesised into a coherent framework linking production parameters to end-use performance. This review critically compares nine interacting process factors reported in the 2020-2026 literature – feedstock characteristics, particle size, moisture content, pyrolysis temperature, residence time, heating rate, pressure, reactor configuration and carbonisation method and evaluates how they govern biochar yield, pore development, surface chemistry and water-treatment performance. Pyrolysis temperature is identified as the dominant controlling factor, consistently governing carbon stability, aromaticity and surface area development, while the remaining parameters exert secondary, largely temperature-dependent effects. The synthesis exposes persistent inconsistencies in reported optimum conditions, weak standardisation of characterisation protocols, and limited linkage between production parameters and specific water-treatment or resource-recovery outcomes. Closing these gaps will require standardised production protocols, digitally controlled process optimisation, life-cycle assessment and application-specific biochar design. Rather than summarising individual studies, this review critically synthesises and compares the evidence base to provide a decision-oriented framework for optimising water hyacinth-derived biochar production for sustainable water treatment and resource recovery.