Last week, Delhi government had sent a report of a fact-finding committee on the water tanker scam to Lt Governor Najeeb Jung.
Delhi's Anti-Corruption Branch on Monday registered a case in connection with the alleged Rs 400-crore water tanker scam linking former Delhi Chief Minister Sheila Dikshit.
ACB chief MK Meena said two complaints were received with regard to the scam and those named in the complaints include Ms Dikshit and Delhi Chief Minister Arvind Kejriwal. He said both Ms Dikshit and Mr Kejriwal will be questioned.
"An FIR has been registered under relevant sections of IPC (Indian Penal Code) and Prevention of Corruption Act and both of them will be quizzed," Mr Meena said.
Last week, the Delhi government had sent a report of a fact-finding committee on the scam to Lieutenant Governor Najeeb Jung.
Delhi BJP leader Vijender Gupta had also filed a complaint with Mr Jung accusing Mr Kejriwal of "suppressing" the committee's report for 11 months.
The Lieutenant Governor had forwarded the committee's report as well as Mr Gupta's complaint to the ACB.
Last week, Delhi's Water Minister Kapil Mishra had written to Prime Minister Narendra Modi and Mr Jung recommending either a Central Bureau of Investigation (CBI) or ACB probe against Ms Dikshit in connection with alleged scam.
"The report of the committee suggests that the acts of omission and commissions by the Delhi Jal Board under Dikshit has resulted in loss of approximately Rs 400 crore to the exchequer," Mr Mishra had said.
Sources said the fact-finding committee found glaring irregularities in the appointment of consultants, tendering process as well as in overall procurement of the tankers by the previous Congress government.
When the tankers were purchased, Ms Dikshit was chairperson of the Delhi Jal Board.
Ms Dikshit has already dismissed the allegations as politically motivated.
Mr Gupta said it was a "moral defeat" of Mr Kejriwal as the ACB was looking into his complaint of delay on the part of the Delhi chief minister in recommending probe into the case.
"He had come to remove corruption but now it appears he himself become a part of it," Mr Gupta said.
Delhi BJP president Satish Upadhyay has welcomed registration of the FIR in the alleged water tanker scam.
The party has demanded Mr Kejriwal's resignation.