When the rivers are in low flow, this impacts on Tararua District Council's ability to take water from the various sources.
In Woodville, the Mangapapa River is at a level where the council is unable to draw any water and is now relying solely on its reserves.
Tararua District mayor Tracey Collis said the reserves were built to store water for times of low river flow.
"Once we are relying on these reserves, water conservation becomes even more crucial.
"It's important that we make the move to alternate evenings now rather than wait for a change. If river flows improve, we will definitely look at decreasing restrictions but right now we have to be proactive in our management of water and respond to the impacts of the hot and dry summer period.
"This proactive approach cannot succeed without the support of our residents. We need everyone to be mindful of their consumption and work together to ensure we all have enough for the duration of the summer months."
If current trends continue as they are, the council may be forced to increase water restrictions to the next level which is a total outdoor ban.
Residents across the district should consider ways to reduce their use, or supplement use by installing water catchment systems.