Of the 81 major reservoirs monitored by the CWC, 36 have significant hydropower capacity of over 60 MW each. Eighteen of the 36 now have less water than the average over the last 10 years at this time of the year. The low levels will affect their ability to produce electricity.
The CWC said in a statement that "the combined live storage in these 81 reservoirs at the beginning of monsoon on June 1 was 11 percent of their designed capacity and stood at 35 percent of the designed capacity on July 30.
"The present storage is 112 percent of last year's storage and 102 percent of last 10 years average storage during the like period," the statement added.
"Out of these 81 reservoirs there are presently 30 reservoirs where this year's storage is 80 percent or less than the average of previous 10 years and in remaining 51 reservoirs the storage is more than 80 percent of the average of previous 10 years."
India gets over 80 percent of its annual rainfall during the monsoon.
The CWC said most reservoirs in south India had more than average storage, those in Orissa and Gujarat were around the average but those in the north were below.
Agriculture ministries in various states are already advising farmers to move to short duration crops that require less water, though their cultivation may be less profitable.
The CWC said it was providing information of the weekly storage position in these reservoirs to the Crop Weather Watch Group "for evolving suitable crop strategies and also appraising the situation to various departments and ministries involved in water resources planning".