This study evaluates phosphoric acid–activated carbons derived from Colocasia esculenta (yam), Ageratina adenophora (crofton weed), and Sechium edule (squash) for fluoride removal from water. The prepared carbons exhibited high BET surface areas of 884.4, 803.2, and 731.5 m²/g, respectively, with well-developed porous structures confirmed by SEM analysis. FTIR spectra indicated abundant oxygen-containing functional groups that facilitated fluoride adsorption. Under optimal conditions, yam-derived activated carbon (YPAC) achieved the highest fluoride removal efficiency (97.2%), followed by CWAC (96.9%) and SPAC (94.7%). Equilibrium data were best described by the Langmuir model for YPAC (R² = 0.995; qmax = 4.29 mg/g) and the Freundlich model for CWAC (R² = 0.997; Kf = 5.44) and SPAC (R² = 0.975; Kf = 4.72), indicating monolayer and heterogeneous adsorption, respectively. Kinetic analysis showed pseudo-second-order behavior for YPAC (R² = 0.996) and pseudo-first-order behavior for CWAC and SPAC (R² = 0.999). Adsorption was favored under acidic conditions, consistent with pHZPC values of 6.3 (YPAC), 6.0 (CWAC), and 5.8 (SPAC). Tests using natural water samples containing 3.2–4.8 mg/L fluoride confirmed effective reduction to below 1.0 mg/L. The results demonstrate that biomass-derived activated carbons, particularly YPAC, are efficient and sustainable adsorbents for fluoride remediation.