TasWater chief executive Mike Brewster said the stage one water restrictions required people to make small changes to their water usage.

"But with almost 100,000 connections in the region, even small changes can have a significant impact on the amount of water available in the system," Mr Brewster said.

"At this point, stage 1 restrictions are deemed to be appropriate and the earlier we can implement them, the less impact there will be on our community over time.

"Even though stage 1 restrictions don't commence until 20 December, we encourage residents, tourists, industrial and agricultural customers - in fact, we ask any user of our systems - to think about how they use water and make small changes where they can."

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TasWater said its decision to introduce restrictions until the end of February was based on advice from engineers and scientists who monitor access to drinking water across Tasmania.

"Our analysis also has to take into account the cumulative effect these factors have not only for this year, but for next year and subsequent years too," Mr Brewster said.

Stage 1 restrictions aim to reduce non-essential water use by 20 per cent.

They include restrictions on when gardens can be watered.

Garden and lawn watering is allowed on any day during the following times: Manual watering systems can only be used between the hours of 6am and 8am and between the hours of 8pm and 10pm.

Automatic watering systems can only be used between the hours of midnight and 4am.

Handheld hoses with a trigger nozzle, buckets or watering cans may be used at any time.