Some of the largest farms in Waikato may be affected by changes to the way water is managed.
Waikato Regional Council says they will have to apply for consents when water is deemed to be in tight supply.
Under changes approved recently by the regional council, municipal users will given priority at times when there is low water flow.
Demand for water has grown substantially in recent years and is forecast to continue. It is driven by rising urban and industrial use, especially in the expanding dairy sector.
The regional council says the current system used to grant water allocation consents - first in, first served - is ineffective, given the need to prioritise supplies for people, businesses and farm stock.
However, it says there will be little noticeable change for most farmers.
