Maybe, a 3% reduction (per each monk level) on what the characters loss per tick (6 minutess) so they experienced a slowly lose of organic resources?
Then, a perfect level 30 monk could only require a 10% of the water and food that other common persons requires to survive...
Real samples:

The modern conditions of life, the heating, the habit of the work, between other reasons, have removed us from this capacity. Though still the last hibernators exist, for example in the Tibet, where the monks on having pondered and to be to low temperatures manage to activate the way hiernación.
On having reduced their metabolic activity, the food and drink needs also diminish of drastic form.
This is something that, in my opinion, fits with Monks and that could help them also in RP meanings
Speaker: "Hey Amadeo, do you never eat or drink? I rarely saw you doing that..."
Amadeo Pneuma: *He directs a calm look for him and with a smile in the face, reply: the one who learns to dominate his body, learns to submit the hunger and the thirst"
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I could give this aswell to the druids reaching the Archidruid rank (elvel 21 druid and above, perhaps) as it is documented in tradition and folklore tales about celtic druids than the highest of them had the ability to hibernate in their groves.
Cheers!