Rotorua water supply pumps are struggling to keep up with demand from users.
Rotorua Lakes Council water operations manager Eric Cawte said water usage from the supplies had "exceeded capacity" last week. An average of 7 million litres was recorded in some areas on several days.
"If this continues over an extended period of time, the reservoirs will run out and water will not be available to consumers."
"If water usage had continued to exceed pumping capacity at the same rate as it did on Monday, the main Eastern and Central reservoirs would have been empty within five to six days. These reservoirs have never run out of water before and we do not anticipate this happening in the near future."
Cawte said most of the water in Rotorua was naturally sourced from springs which meant there was a constant supply of water. The exception was Rotoma, which was supplied from the lake, and Mamaku, which was supplied from bores.
However, there was a limit to how quickly and how much water could be pumped and stored on a daily basis.
While the supply from the springs were not affected by the low rainfall, the pumps were "struggling to keep up" with demand.
The heatwave last week, meant water was being used faster than it could be pumped from the springs.
"It is important to maintain a reasonably high level of water in the reservoirs to ensure we have enough stored in the event of a pump breakdown."
Cawte said residential properties were responsible for 70 per cent of the water usage, more than double the commercial water usage at 30 per cent.
"[People] are noticing their gardens and lawns are looking dry and so they have started to water these, whereas two or three weeks ago they weren't necessarily doing so."
Rotorua had its hottest January on record since 1964 with an average temperature of 26.5C with a light pittering of 44mm of rain.
"While there has been an improvement ... a couple of big consumption days can quickly set us back, and weekends have traditionally shown higher consumption than weekdays."
Rotorua resident Tania Garland said she was surprised when she saw council-owned flowerbeds outside Pak'n'Save being watered at midday on Tuesday.
"I just thought it was crazy with the weather, in the middle of the day, to have sprinklers going. Then to ask people of Rotorua to conserve water," Garland said.
Last Tuesday was Rotorua's second-hottest maximum temperature on record at 31.4C.
Cawte said the council had not banned using sprinklers or watering gardens at this stage.
"However, we do ask that [people] keep this to a bare minimum, and consider letting lawns go brown, as they will recover after the next significant rain.
"Council is also expected to be aware of water usage and we are trying to keep our watering to a minimum."
Lux Organics managing director Jenny Lux said water was critical to the livelihood of the small family farm which had never experienced a hot, dry summer in their two and a half years of operating.
Lux said they always calculated exact amounts of water needed, but if a water restriction did occur, they would need to prioritise the younger plants.
Federated Farmers' Rotorua/Taupō provincial president Alan Wills said their rural water supplies were metered and separate from the town supply.
Wills had never experienced a water restriction.
ABC Rotorua Central Childcare manager Tina Bunyan said it was important to keep the children they cared for, aged 3 months to 5-year-olds, cool in the heat.
While they had water-play, they did activities in the airconditioning at the hottest times of day and filled buckets of water instead of using hoses to cool down.
Fire and Emergency New Zealand Central Lakes assistant area commander Hamish Smith said FENZ was well aware of the water demand and had tried to limit its water use from the council supply.
This was done through a limit on water-based training, hose washing and testing which involved water, and only used water when essential.
Smith said they had been lucky there were no large fires during the hot, dry weather.
"Water supplies also have an emergency amount calculated within their reserves for the purpose of firefighting," Smith said.
Rotorua Lakes Council will notify the public in the event of any water restrictions.
• Keep watering gardens to a minimum: a hand-held hose is better.
• Keep lawns longer: that creates deeper roots and retains water.
• Do not leave sprinklers on overnight.
• Only water areas that need it.
• Hoses use a lot of water: avoid washing cars, houses or driveways with them and use a bucket and sponge instead.
• Don't unnecessarily run taps.
• Fix any leaks on your property promptly.
• Look out for water leaks in unusual places.
• Call the council on (07) 348 4199 if you see leaks in the street.