With dry weather predicted over summer, and flows in all Otago rivers already low, the regional council is advising irrigators to implement conservative practices.
Council manager of environment services Martin King says all rivers, except the Clutha/Mata-Au are falling towards minimum flow levels.
A number, including the Kakanui and Shag, are already at levels not usually seen until late summer.
Mr King says if no substantial rain falls throughout the region soon, rationing may need to begin later this month or early in the new year.
