The adsorption of heavy metal ions from surface water with ecologically safe and biodegradable biopolymers is increasingly becoming an appealing research challenge. Starch as a biopolymer is exceptionally attractive to solve this problem for its low cost and abundant availability in nature. To expel Ni²⁺, Fe^2+/3+, and Mn²⁺ from water, we analyzed two native and two oxidized starches, namely potato and corn starch, as bio-adsorbers. The morphology and the surface property of the different starches were studied using SEM. To assess the effectiveness of adsorption onto the starches, we tested three realistic concentrations based on German drinking water ordinance values that were 10-fold, 100-fold, and 1000-fold the limits for Mn²⁺, Fe²⁺, and Ni²⁺, respectively. The concentration of the different ions was measured using the ICP-OES. Furthermore, from subsequent investigations of the adsorption isotherms, we evaluated the adsorption capacities and mechanisms. The adsorption isotherms were fitted using the Langmuir, Sips, and Dubinin–Radushkevich models, whereby Sips showed the highest correlation. Oxidized potato starch achieved viable adsorption capacities of 77 µmol Fe²⁺/g, 84 µmol Mn^2+/g, and 118 µmol Ni^2+/g. Investigating the influence of initial swelling in water on the adsorption performance, we found that especially the percentage removal with oxidized starches decreased significantly due to the formation of hydrogen bonds with water molecules at their binding sites with prior swelling.