"One of the indicators is the level of the Mangateretere Stream, which has dropped to near its minimum level, triggering the first stage of restrictions," an HDC spokeswoman said.
The council is also reviewing its watering programmes for its parks and gardens in the same way that gardeners are being asked to.
Hours of watering are being reduced and moved to the coolest times of the day at parks and gardens supplied from the public system.
Some public parks and private green spaces, including the Hawke's Bay Racecourse and the Showgrounds Hawke's Bay Tomoana, have their own bores and are not subject to the restrictions.
To help conserve water, the council suggests checking for leaks and fixes any leaking taps, pipes or cisterns, use 'eco' settings on dishwashers and washing machines, scrape dirty dishes rather than rinsing and turn off taps while brushing teeth.
While outside the home, the council suggested using a directional sprinkler, reuse 'grey water' from the washing machine on lawns and gardens, use a bucket of water when washing the car and use a broom to clean paths rather than hosing.