An apparatus for determining an amount of chemical input, comprising: an information-receiving unit configured to receive environmental information, chemical information, and water-quality information of the water present in a specific area; and a chemical input determination unit configured to derive a multiple regression equation based on the received environmental information, chemical information, and water-quality information and to determine a future amount of chemical input to satisfy a target turbidity of the water present in the specific area based on the multiple regression equation, wherein the chemical input determination unit is further configured to derive a relation between a future water turbidity, which represents a future turbidity of the water present in the specific area, and the future amount of chemical input based on the multiple regression equation, and to calculate the future amount of chemical input based on a significance level and the future water turbidity, and wherein the environmental information is a current temperature of the water present in the specific area, the water-quality information is a current turbidity of the water present in the specific area, and the multiple regression equation is represented by Equation 1: Δ ⁢ Turb t − ρ ⁢ Δ ⁢ Turb t − 1 = C 0 + C 1 ∗ Turb t − ρ ∗ Turb t − 1 + C 2 ∗ F t − ρ ∗ F t − 1 + C 3 ∗ S t − Tmp t − ρ ∗ S t − 1 ∗ Tmp t − 1 + C 4 ∗ S t ∗ Turb t − ρ ∗ S t ∗ Turb t + ε t wherein ε(t)=e(t)- ρ ∗ e ( t -1), ε(t)∼ N (0, σ 2), e(t) is a residual, Turb is a turbidity of the water, F is a concentration of iron chloride, S is a concentration of sulfuric acid, Tmp is a temperature of the water, t represents a future time point, t-1 is a current time point, Δ is a change, ρ is an autocorrelation coefficient, and C0 to C4 are regression coefficients. an information-receiving unit configured to receive environmental information, chemical information, and water-quality information of the water present in a specific area; and a chemical input determination unit configured to derive a multiple regression equation based on the received environmental information, chemical information, and water-quality information and to determine a future amount of chemical input to satisfy a target turbidity of the water present in the specific area based on the multiple regression equation, wherein the chemical input determination unit is further configured to derive a relation between a future water turbidity, which represents a future turbidity of the water present in the specific area, and the future amount of chemical input based on the multiple regression equation, and to calculate the future amount of chemical input based on a significance level and the future water turbidity, and wherein the environmental information is a current temperature of the water present in the specific area, the water-quality information is a current turbidity of the water present in the specific area, and the multiple regression equation is represented by Equation 1: Δ ⁢ Turb t − ρ ⁢ Δ ⁢ Turb t − 1 = C 0 + C 1 ∗ Turb t − ρ ∗ Turb t − 1 + C 2 ∗ F t − ρ ∗ F t − 1 + C 3 ∗ S t − Tmp t − ρ ∗ S t − 1 ∗ Tmp t − 1 + C 4 ∗ S t ∗ Turb t − ρ ∗ S t ∗ Turb t + ε t wherein ε(t)=e(t)- ρ ∗ e ( t -1), ε(t)∼ N (0, σ 2), e(t) is a residual, Turb is a turbidity of the water, F is a concentration of iron chloride, S is a concentration of sulfuric acid, Tmp is a temperature of the water, t represents a future time point, t-1 is a current time point, Δ is a change, ρ is an autocorrelation coefficient, and C0 to C4 are regression coefficients.