The growing demand for environmentally compatible water-treatment technologies has increased interest in bio-based coagulants as alternatives or complementary agents to conventional chemicals. This study evaluated polysaccharide-containing extracts from Opuntia ficus-indica and Subpilocereus repandus against polyaluminum chloride (PAC) using coagulation–flocculation jar tests with synthetic and natural raw-water matrices. In synthetic water (729 NTU turbidity; 610 Pt–Co apparent color), both cactus-derived biocoagulants showed their highest clarification performance at 10 mg/L. Opuntia ficus-indica achieved 94.65% turbidity and 83.33% apparent color removal, while Subpilocereus repandus achieved 89.49% and 73.72%, respectively. PAC produced faster clarification and higher overall removal; at 16 mg/L, turbidity and apparent color removals reached 99.81% and 99.51% after 60 min. In the exploratory natural raw-water assessment (41 NTU; 301 Pt–Co), Subpilocereus repandus at 10 mg/L achieved 97.12% turbidity and 90.03% apparent color removal. Cactus-derived extracts showed dose- and time-dependent behavior with limited pH variation. COD initially increased after cactus-extract addition, reflecting oxidizable organic matter introduced by the extracts, then decreased during treatment. These findings support their potential as alternative or complementary materials for water clarification.