The incidents were reported from Dahisar, Kandivli, Malad and Dadar areas, a senior police official said.
While two were washed away in nullahs, one was washed away in a drain and the other was washed away during Ganesh idol immersion proceedings, he added.
In another incident, one person Rameshwar Tiwari was killed after the wall of a power sub-station fell on his house in Asalpha village in suburban Ghatkopar, police said.
His 35-year-old wife and nine-year-old son sustained injuries in the incident that took place in the early hours, they added.