The dynamic relationship between particle size distribution and water turbidity was characterized using online real-time monitoring devices to explore the impact of particle size distribution on water quality. Particle amount was proportional to water turbidity in the range of 0-40 NTU, whereas the correlation was rather poor in the range of 40-100 NTU. The number of particles smaller than 5 mu m (N-d (< 5)) should be strictly monitored and controlled in water treatment works (WTWs) due to their complex behaviors. The fractal dimension of particles (d(pf)) is well suited to characterize particle size distribution under different water turbidities. The first derivative of d(pf) was firstly used to explain the relationship between d(pf) and the percentage of N-d (<) (5), and the turbidity and d(pf) values could be used together to monitor the temporal evolution of the number of smaller particles. A new block method for analyzing flocculation processes was proposed based on the change in d(pf). The particle counting method was more sensitive to the evolution of particle size, which allowed a better understanding of the impact of particle size distribution on water turbidity. (C) 2014 Elsevier B.V. All rights reserved.