This paper reports the potential of watermelon seed as a natural coagulant for water treatment. It was aimed at identifying watermelon seed as a possible replacement for alum and other synthetic polyelectrolytes in treating water. Laboratory scale studies using jar test experiments were performed on medium turbid water to determine the effect of dosage, pH stirring time and speed on coagulation. Results obtained showed that at dosage of 0.1g/L, pH of 7.0, stirring time of 8 minutes and mixing speed of 100rpm, optimal removal of turbidity was obtained. The reduction in turbidity was below the world health organizations (WHO) recommended value of 5NTU, however the best colour removal was not up to the WHO recommended value of 40TCU. When used in combination with alum, it caused unfavourable changes in the pH of the treated water however with 20% alum as coagulant aid, the best colour and turbidity removal at acceptable pH was obtained, with residual turbidity of 0.89 NTU and residual colour of 15TCU at a pH of 6.50. The results showed that watermelon seed can be used as a natural coagulant for water treatment.