The suspended Bharatiya Janata Party MLA was picked up under Act No.1 of 1986 (Preventive Detention Act), police said.
Singh, known for his hardline religious rhetoric, was suspended by the party following protests in Hyderabad against his comments leading to his arrest by the Telangana Police.
A case has been registered in Hyderabad against Telangana Bharatiya Janata Party MLA Raja Singh for his remarks which allegedly defended the attacks on Dalits in Gujarat's Una and supported the cow vigilantes involved.
Majlis-e-Ittehadul Muslimeen MLA Akbaruddin Owaisi, accused of sedition for his "hate speech", was on Monday booked in a similar case, police said.
As many as 25 people were arrested so far in connection with the communal violence that erupted in the city last week, the police said on Thursday.
The latest rains since Saturday evening led to lakes and other water bodies overflowing and triggering flooding of several low-lying areas, including places affected last week, in Hyderabad and on the outskirts.