Recently enormous exertions have been dedicated to modify graphitic carbon nitride (g-C3N4)-based photocatalysts via morphological adjustment and compositional control, providing various ways for the advance of high-efficiency catalysts in the field of photocatalytic water purification. This review summarizes the latest developments in photocatalytic removal of contaminants and sterilization in water with g-C3N4-based materials, highlighting the performance and mechanism of multi-component cooperative photocatalysis. We review various strategies for improving the catalytic performance of g-C3N4-based photocatalysts, introducing theoretical calculations to explore the relationships between basic properties and photocatalytic activity. Then the performance and mechanism of photocatalytic water purification with g-C3N4-based materials are discussed. Finally, we put forward the principles and ways for the enhancement and application of g-C3N4-based composites in the future, evaluating their full life-cycle in photocatalytic water purification.