Abstract: Colorimetric method is one of the common methods used for the environmental monitoring of Arsenic on-site. However, the results that are mainly based on interpretation of the operator are less accurate and reliable. This study describes a more reliable approach to determine Arsenic (V) concentrations whereby an image processing technique is incorporated into a colorimetric method. In this approach, Arsenic (V) concentrations are quantitatively determined by digitized the color formed by the reaction of arsine gas generated from the ion with silver ion impregnated on the filter study. Multiple regression analysis is used to develop a mathematical model to analyze Arsenic (V) concentration by Minitab software. Validation of the developed mathematical model is performed by evaluating the model with the data from the Arsenic (V) standard solutions. The developed mathematical model to determine Arsenic (V) concentration is: Arsenic (V) concentration = 916-2.19 Red -2.30 Green -1.667 Blue. The correlation between the calculated Arsenic (V) and known Arsenic (V) concentration was high (R2 = 0.9997). The results also revealed that relative bias (0.2 to 3.8%) and relative standard deviation (0.2 to 2.7%) of calculated Arsenic (V) concentrations are low. The accuracy of the Arsenic (V) concentration estimation by the model is between 96 to 99%. It can be concluded that the developed mathematical model is able to estimate the Arsenic (V) concentration accurately and precisely.