The woman fell into a 'nullah' filled with rainwater in Kalwa and drowned, officials in the Disaster Management Cell of the Thane Municipal Corporation (TMC) said.
The deceased, Sainath Shaikh, was a housewife who resided in Shanti Nagar.
In the second incident, 14-year-old Gauri Jailwar died after falling into a swollen drain near a mall here, they said.
Two women were injured when the compound wall crashed on houses located in the Manpada locality, the officials said.
Several houses were also damaged, they said.