Natural plant extracts have been used for water purification for many centuries. Most of these was derived from seeds, leaves, bark or sap, roots and fruits of trees and plants. In this paper, using seed powder of Cassia fistula as natural coagulant, establishing their optimal dose through “jar tests” and determining the parameters of color, turbidity, total alkalinity and total hardness, using water from the “Canal del Dique”. The optimal effective dose of coagulant is found between 15-25 mg/L, obtaining final values of turbidity and color of 6 NTU and 25 UC respectively. The pH values no major variations, as total alkalinity. The values of the parameters turbidity and color are located near the standards set by the Colombian standard to ensure the quality of water for human consumption, as well as the pH, total alkalinity and total hardness, demonstrating the potential use of this coagulant primary natural coagulant in water treatment.