"Delhi will get an additional 150 cusecs up to June 30 if it takes back cases in the National Green Tribunal and the Delhi High Court," Mr Khattar wrote to Mr Kejriwal.
Replying to a letter from Mr Kejriwal, Mr Khattar said Haryana had been supplying about 1,050 cusecs of water from the Munak canal "when Delhi decided to drag Haryana into multiple litigations".
Upon a request from Water Resources secretary, Haryana then started releasing an additional 150 cusecs from Munak, so that about 100-120 cusecs may be received at Wazirabad, he said.
"We have decided to extend the period of release of this additional water via DD-8 up to 30 June, 2018 subject to the condition that Delhi withdraws all cases from the NGT and Delhi High Court," Mr Khattar said in a "demi-official" letter released here by Haryana government.
It said "multiple litigation" was waste of time and energy and added, "I hope that in case of litigation by private persons, you would defend Haryana's stand of Upper Yamuna River Board (UYRB) being the correct forum for deliberations and decision-making on such issues."
Mr Khattar said the national capital's claimed shortage of 60 million gallons per day (MGD), can easily be resolved by Delhi Jal Board (DJB) itself, saying the agency had a total water treatment capacity of 900 MGD.
"We have acceded to request of Secretary, Ministry of Water Resources (MoWR) to supply 120 cusecs through DD-8 for the current summer only. Delhi must make its own arrangement from the next year onwards as no supplies would be made through DD-8 by Haryana on account of reasons explained in detail in our reply before the Supreme Court," he wrote.
"We have been discharging all our obligations set forth by Upper Yamuna River Board (UYRB) in terms of share and allocation of water to Delhi," he said, while pointing at the "acute shortage" of water in Yamuna.
He said despite the adverse impact on drinking water supply to thousands of Haryana villages and several towns, the state had never reduced the supply to Delhi.
"In fact, presently we are supplying 120 cusecs over and above our obligations," he said.