The water quality of our seas has been decreasing dramatically over the few years and pollution of heavy metals is believed to be the reason in Hong Kong and all over the world. In our investigation, we aim to design an efficient kit in terms of time and cost, which is used to detect common heavy metals or harmful ions that can be found in water. Most of the ions had a linear relationship with the RGB values for creating a standard curve to determine the concentration of the particular ions in the water. In the study, some of the tests for ions may not be specific enough and may be reacted with some non-specific ions and thus interfered with the colour change. This leads to a decrease in sensitivity for certain ions. Nevertheless, some brief information on whether the water is drinkable can be provided using the kit, and thus the quality of water can be known.