Fig. 4.

The possible water transmission routes and the migration mechanism of viruses. Viruses excreted in 1) feces and urine of patients are collected and transported by 2) sewage pipe network, and subsequently enter the 3) wastewater treatment plant (WWTP). Viruses may be discharged with 4) sewage effluent to surface water in case of malfunction. 5) Reclaimed water applied in spray irrigation, cooling towers and toilet flushing may carry viruses. Viruses excreted in feces and urine are treated by 6) septic and transported into groundwater. Viruses adsorbed on 7) domestic garbage (e.g. masks and kitchen waste) enter the runoff via rainwater. Viruses survived in intake water would be treated with a range of physical, biological, and chemical processes in 8) drinking water treatment plants (DWTP) and transported to residential area by 9) water distribution system.