The present disclosure provides a color chart and a test kit for estimating chemical oxygen demand of water. The color chart includes a blue component, an indigo component, an umber component, and an orange component. The test kit includes an oxidant, a reductant, an indicator, and the color chart. The present disclosure also provides a method for estimating chemical oxygen demand of water. The method includes providing a water sample; adding an oxidant to the water sample; heating the water sample; adding a reductant to the water sample; adding an indicator to the water sample, such that the water sample develops a color; and matching the color of the water sample with the color components of the color chart to estimate the chemical oxygen demand of the water sample.