MidCoast Council estimates that if water restrictions were to remain at level three, there would be between 80-90 days of supply in Bootawa Dam.
According to Rob Scott, council's director of infrastructure and engineering services, council stopped pumping from the Manning River to fill the dam on October 11.
Bootawa Dam's capacity has been falling since that date and is currently at 90 per cent, Mr Scott said.
"It does seem like a really striking figure and for people who hear that figure for the first time it will be an absolute shock because everyone would think that we have a lot more storage than that," Mr Scott said.
Level three water restrictions are being introduced on Monday, with stricter restrictions possibly being introduced in coming weeks.
"I don't know exactly how far we could stretch it, because we don't really know how effective it would be to amp water restrictions to no external water use whatsoever.
"But when the chips are really down, we would absolutely knuckle down and get rid of all external water usage and really start to restrict internal water usage," Mr Scott said.
"Exactly how far we would get out of that, at the same time, is difficult. We'd also look at ramping up the Nabiac acquifier supply."
Mr Scott said the Nabiac acquifier is now being used.
"It's well below its capacity at the moment. We're conscious of not trying to get in too early and use it all and use it to early," he said.
Council is currently in the process of renegotiating its water access licence conditions with the National Resource Access Regulator to allow it to pump from the river to "maximise their yield".
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