This study describes how physicochemical characteristics of rice straw-based biochar, prepared at a different pyrolysis temperature (550, 650, 750 degrees C) and treated by HNO3 or H2O2 or KMnO4, influence on its removal capacity for fluoride, nitrite, and nitrate anions from the water. Biochars exhibit broad pore size distribution from wide mesopores (5.0 nm) to narrow micropores (1.0 nm). Furthermore, all prepared biochars have both basic sites (2.8-8.13 meq/g) and acidic ones (1.8-9.3 meq/g) on their surface. The effect of biochar porosity, acidity, and basicity on anions adsorption was studied. KMnO4- and H2O2-treated biochar give high nitrite and nitrate uptake in micropore range (0.03-0.05 cc/g) and mesopore range (0.01-0.06 cc/g) while HNO3-treated ones give low uptake in both micropore range (0.02-0.021 cc/g) and mesopore range (0.01-0.05 cc/g). As a conclusion, no particular characteristics seem to be an influential essential in the removal of anionic contaminants. These observations are useful to guide the surface modification of biochars as efficient sorbents for specific application needs and removal of environmental pollutants.