Water purification is the recent emergence in handling sewage and contaminated solution from different sources, such as industrial and domestic disposal. Such practice is being comprehensively explored to foresee whether it could be applicable in our lives since a couple of unpredicted toxic chemicals in wastewater may pose a significant risk to people. Environmentally-friendly research on water purification stands out as a promising solution, therefore, water purification by utilizing natural sunlight and nanomaterials was proposed by scientists. This thought incorporates raw environmental resource into chemical reaction of chosen materials. Literally, photocatalytic water purification is the decomposition of organic solution into less harmful products under the irradiation of sunlight. To quickly realize how photocatalytic reaction is proceeding in a compact and observable scale, a small-size of solar reactor could also be fostered because of its high surface to volume ratio. Consequently, Wang et al.¹ claimed that the technology is undergoing rapid development due to its tremendous potential in the fast testing field in environmental science. In the essay, the mechanism and its diverse application of light-induced water purification by using catalysts in micro-reactors will be discussed in an ordered manner.